I've been playing around with rebuilding these for some time now, with the goal of having a cotton wick instead of silica. I finally have a process that, so far, has reliably worked for me that I thought I'd share. Sorry for the long post.
What you'll need:
1) 100% cotton yarn, #4 size (I use white Peaches and Cream from Wal-Mart)
2) Kanthal A-1, 32 gauge for the coil
3) A small piece of spare Kanthal, say 3 inches long, to act as a needle threader.
4) A 2-56 screw. You can get these as pushrods or pushrod ends at a hobby store, especially ones that specialize in RC airplanes.
5) A vise is useful to hold the screw/threaded end to free up both hands for wrapping the coil, although not totally required.
6) a Bic lighter (or equivalent).
7) A straightened-out small paper clip, or a relatively small sewing needle.
First, boil your yarn for at least 20 minutes or so, changing the water a few times. Allow to dry.
Take your small piece of spare Kanthal, bend it it half, and twist half of it together tightly. This will make a loop, that looks similar to, well, a sperm (we're all over 18, right?

). You'll use to thread your cotton yarn through the coil... in essence, a cheap needle threader.
Cut 4-5" of Kanthal from the spool, and run the lighter under the length of it a few times.
Using the 2-56 screw, tightly coil the Kanthal around it, using the threads as a guide. Don't miss any threads, as you want the coil to be tightly and evenly spaced. 5 wraps equates to about 2.4ohms. You want both ends to be pointing down when you're done.
Holding and pulling the ends straight down very tightly, while the coil is still on the screw, heat the coil/screw with the lighter for a few seconds. This will "set" the coil. Once cooled down, "unscrew" the coil off the screw.
Cut a 2-3" piece of your pre-boiled yarn, and separate the 4 individual threads of the yarn.
Feed the ends of the (now separated) threads through the loop of your needle threader, then double the yarn back. You only need to double-back maybe 1/2" or so of it, just enough for you to pinch so it doesn't slip out of the loop of the needle threader.
Pinching the yarn tightly where it is doubled back, feed the twisted end of your needle threader through the coil, then pull the coil onto the yarn. It will be a bit tight until it clears the "double backed" section, then will slide easily.
Center the coil roughly, remove your needle threader.
Slide the paper clip/needle through the coil, parallel to the yarn threads.
Grab your empty Nova head, feed the coil ends down through it until the paperclip down to the very bottom of the slots. This paperclip will help you keep the coil centered vertically as well as horizontally while you assemble the bottom end.
Assemble the grommet and push-pin as normal, using the paper clip to keep everything centered. I usually push down on the paper clip with one hand (holding it tightly against the bottom of the slots) while I push up on the push-pin with the other. This prevents the leads from slipping and popping the coil/wick up out of the head.
Remove the paper clip, center your wicks, do any last-minute adjustments to the coil (center it in the head, make sure they don't touch each other or the outer head), screw onto the base, and cut the wicks to the correct length.
Vape away! You will notice slight cottony/muted flavor for about the first 20 vapes or so, but the flavor will come through very cleanly after about 1/2 tank. Longevity depends on the juice... I have one that is still going strong after 3 weeks of pretty constant vaping (it's my favorite juice at the moment), while another juice (RY4) kills them in about 1 to 1.5 weeks.
Hope this helps...