To start, I am unable to post in the modding forums, so can a moderator move this thread for me?
I do not have a working camera to get pictures of the process on here, so I will have to make do with descriptions. If someone that decides to undertake this process can and wants to post pics, that would be great.
I started by ordering my PCC from litecigusa.net along with some XL carts to try out. I mention litecigusa.net so that others will know exactly what PCC and XL carts I am using (I understand there are several kinds of both). I discovered that the XL carts, with the original rubberish cap-plugs would fit in the case and the lid would close. However, this was not the case with an assembled atty/cart. I needed to have about 1mm more room to close the lid on the PCC completely with an assemebled atty/cart.
All of the instructions are written so that the front of the PCC has the display, button and led.
The process:
1) Remove all E-Cig components (carts, atty/cart, and batteries)
2) With the foam insert still in place, use a fine tip pencil to draw a circle on the plastic where the atty/cart is to go. I chose the slot at the front right (closest to you and farthest to the right when the lid is flipped open and back, with the lcd facing you). You may or may not be able to use another slot, try the others at your own risk, as the battery/circuitry block may not fully support the carts in other locations.
3) Remove the foam insert. Mine was not glued in, simply wedged in. A pair of tweezers or a paperclip will help in removal.
4) Remove the 2 screws under the insert (located in the back right area, and front left area). You will need a small screwdriver for this. Set the screws in a safe place so you don't lose them
5) Carefully remove the bottom plate (where you would plug in the power supply to charge the pack). The plate consists of the bottom cover, 2 screw mounting cylinders (where the screws connect), and a plate that seems to serve as a spacer to hold the circuitry block in place. Set this piece aside in a safe place.
6) This is likely the hardest part of the process, and the step where you are most likely to damage the PCC. VERY CAREFULLY pry the front of the PCC (the side with the display) away from the circuitry block so that the button and led will not get hung up on their respective holes as you slide the block out. My block seemed to be lightly glued, possibly double sided tape, Just wiggle it carefuly to loosen this glue/tape. Be mindful of the wires and try not to put ANY stress on them. Slide the block out. There will be 2 wires that stay connected the entire time. The silver plastic button top will probably fall off
, just set it aside. Don't worry its not broken. 
7) While having the case and the circuitry block sitting in a way that will not stress the wires, cut your hole in the spot where you drew your circle in step 2. I used a dremel tool with a grinding bit that was about the diameter of the m401 and about 1/2 inch long. Make your hole slightly larger than your drawn circle. The hole I made turned out to be about 12mm, this seemed to be a good size, since my hole was a little off center of where it needed to be.
7) NOTES: Avoid drilling this hole. Drilling plastic typically ends with the drill bit 'biting' the plastic and acting like a screw, usually destroying the component you are drilling as well as slicing/stabbing any fingers, hands, or other appendages that happen to be near by. Also avoid grinding for long periods of time (more than a few seconds) as this usually melts the plastic, as opposed to grinding it. Melting is bad, it may deform the surrounding areas, making the rest of the parts not fit quite right.
8) Clean the case. Get as much of the plastic dust out as possible, especially around the LCD area and the charging connector (where the battery screws in to charge). Compressed air will probably work just fine for cleaning. I used organic air sacks (lungs) to blow air into the case.
9) Re-assemble the case in the opposite order with one exception, the silver plastic button top. Before sliding the circuitry block back into the case, hold the case front down (so the LCD screen is facing the floor) and place the button top in its hole from the inside of the case. If you are looking through the bottom of the case, it will be the left hole. Once the button top is in place, slide the circuitry block back in until the led is close to the case. Then VERY CAREFULLY pry the front of the case away from the circuitry block so that the Led will clear the inside of the case. Continue to re-assemble everything else in reverse order. BE MINDFUL OF THE WIRES.
Once you get everything put back together, including the foam, the hole you drilled shouldn't be visible (except maybe a small white circular sticker on the top of the circuitry block), and that small layer of plastic you have removed should be just enough for the atty/cart combo to fit correctly and allow the case to close completely.
I hope this serves many of you well. Enjoy.
I do not have a working camera to get pictures of the process on here, so I will have to make do with descriptions. If someone that decides to undertake this process can and wants to post pics, that would be great.
I started by ordering my PCC from litecigusa.net along with some XL carts to try out. I mention litecigusa.net so that others will know exactly what PCC and XL carts I am using (I understand there are several kinds of both). I discovered that the XL carts, with the original rubberish cap-plugs would fit in the case and the lid would close. However, this was not the case with an assembled atty/cart. I needed to have about 1mm more room to close the lid on the PCC completely with an assemebled atty/cart.
All of the instructions are written so that the front of the PCC has the display, button and led.
The process:
1) Remove all E-Cig components (carts, atty/cart, and batteries)
2) With the foam insert still in place, use a fine tip pencil to draw a circle on the plastic where the atty/cart is to go. I chose the slot at the front right (closest to you and farthest to the right when the lid is flipped open and back, with the lcd facing you). You may or may not be able to use another slot, try the others at your own risk, as the battery/circuitry block may not fully support the carts in other locations.
3) Remove the foam insert. Mine was not glued in, simply wedged in. A pair of tweezers or a paperclip will help in removal.
4) Remove the 2 screws under the insert (located in the back right area, and front left area). You will need a small screwdriver for this. Set the screws in a safe place so you don't lose them
5) Carefully remove the bottom plate (where you would plug in the power supply to charge the pack). The plate consists of the bottom cover, 2 screw mounting cylinders (where the screws connect), and a plate that seems to serve as a spacer to hold the circuitry block in place. Set this piece aside in a safe place.
6) This is likely the hardest part of the process, and the step where you are most likely to damage the PCC. VERY CAREFULLY pry the front of the PCC (the side with the display) away from the circuitry block so that the button and led will not get hung up on their respective holes as you slide the block out. My block seemed to be lightly glued, possibly double sided tape, Just wiggle it carefuly to loosen this glue/tape. Be mindful of the wires and try not to put ANY stress on them. Slide the block out. There will be 2 wires that stay connected the entire time. The silver plastic button top will probably fall off

7) While having the case and the circuitry block sitting in a way that will not stress the wires, cut your hole in the spot where you drew your circle in step 2. I used a dremel tool with a grinding bit that was about the diameter of the m401 and about 1/2 inch long. Make your hole slightly larger than your drawn circle. The hole I made turned out to be about 12mm, this seemed to be a good size, since my hole was a little off center of where it needed to be.
7) NOTES: Avoid drilling this hole. Drilling plastic typically ends with the drill bit 'biting' the plastic and acting like a screw, usually destroying the component you are drilling as well as slicing/stabbing any fingers, hands, or other appendages that happen to be near by. Also avoid grinding for long periods of time (more than a few seconds) as this usually melts the plastic, as opposed to grinding it. Melting is bad, it may deform the surrounding areas, making the rest of the parts not fit quite right.
8) Clean the case. Get as much of the plastic dust out as possible, especially around the LCD area and the charging connector (where the battery screws in to charge). Compressed air will probably work just fine for cleaning. I used organic air sacks (lungs) to blow air into the case.
9) Re-assemble the case in the opposite order with one exception, the silver plastic button top. Before sliding the circuitry block back into the case, hold the case front down (so the LCD screen is facing the floor) and place the button top in its hole from the inside of the case. If you are looking through the bottom of the case, it will be the left hole. Once the button top is in place, slide the circuitry block back in until the led is close to the case. Then VERY CAREFULLY pry the front of the case away from the circuitry block so that the Led will clear the inside of the case. Continue to re-assemble everything else in reverse order. BE MINDFUL OF THE WIRES.
Once you get everything put back together, including the foam, the hole you drilled shouldn't be visible (except maybe a small white circular sticker on the top of the circuitry block), and that small layer of plastic you have removed should be just enough for the atty/cart combo to fit correctly and allow the case to close completely.
I hope this serves many of you well. Enjoy.