you can pull the 1000 nub just off the psp, no need to disassamble or anything, it has a square form underneath.
now you can do two things, take a needle stick it it in the c stick and jank it out, it's holden in by 2 rubber circles one on the bottom left and one on the top, jank it out it doessent matter if you destroy the circles you can still place it back in without it falling out. the second thing you can do is open up your 3ds and remove the 3 screws that old the c stick in place and remove the rubber like that.
the form that the holder of the c stick has is a 95% match of that of the psp 1000 nub,i've glued mine in, but it even holds without glue, i just liked the stability of the glued version, you can find it on youtube, try psp c stick mod or something like that, it should work on both models of the new 3ds, i've only done it with my xl yet since i don't have another set of nub's i only have psp 2000 left, i have orded more for my girlfriend's new 3ds but i haven't done those but i've seen other people do them