First off, you'll need a third-party controller (Yobo, Retrobit, etc.) before you do anything to the analog stick. The first-party one uses some sort of optomechanical system, like a ball mouse, that isn't compatible with the pots used in every other controller I'm aware of.
Ah, Dang. I remembered seeing a better one on here somewhere, but didn't bother to take more than a cursory look at the mega-sticky (that's where I got the second link from). My apologies, and yeah, use that one.