Not sure if this helps, but I remember reading somewhere (Pretty sure it was from "The Secret to Teen Power" book) that a guitar player once cut his hand on a sander in wood-shop class, making it impossible to play his guitar (From what the doctor said). Not agree to that, he spent hours everyday trying to move his fingers and soaking it in water. After six months or so of that his hand healed fully. His doctor said he's shocked that it can even move at all.
So maybe long term belief, and practice. But of course to a certain limit (you won't heal a lost hand no matter how much you believe and try.)