no idea if this will help chronic shoulder pain, but my grandma taught me this trick for neck/shoulder cramps: digging your fingertips as firmly as you can into the area right on top of your back, on the side of the area that hurts, drag hard (don't use your nails obviously! in fact maybe clip them if you have very long nails) raking across the muscle grain of the muscles that are sore. repeat three times, let it rest a half minute, repeat three times, rest, continue til it feels better.

this is a grandpa cure (tm) so take it with a grain of salt. it has always worked for me if i wake up with a neck cramp from sleeping in a bad position and/or bad positure at the computer (i tend to scrunch my shoulders horribly when stressed, which is exactly when i'll have to be at my computer fighting to a deadline).