Whenever you get the pains, try to warm your hand up. Stick it under your armpit or between your thighs, or run it under warm water if you've got that. Try to relax yourself. Have you ever tried meditating? That can help. If you've got something like a ball or other object you can curl your whole hand around, try working and flexing with that. It might help trick your brain into thinking that that phantom finger's getting a workout.