This is actually about as easy as it gets.
Look straight down at the center pin and using either a very small flat head screwdriver or pick and lightly, without damaging the o-ring (these are replaceable if you do damage it) until the center post is out far enough for you to pull it out. I highly recommend pulling it ALL of the way out and taking a very small piece of electrical tape and insulating the underside of the center pin, this will resolve future problems you might have with outrageous 9.9 resistance checks. Once you have put the piece of electrical tape in, push the center pin down until it is almost in place and then allow your carto to set the pin the rest of the way.
I am the least bit technically inclined when it comes to hardware, and it wasn't difficult for me. I can take pictures for you if you would like!
