I know nothing about RSI, but if nothing else, it's something you can try for cheap/free (assuming you have a suitably-sized receptable and lots of rice). And if it doesn't help, you can always cook and eat the rice? *g*

This may not be applicable to you as it's very much about my sensory processing issues, but I find it quite soothing; it's nice repetitive motion with heavy massaging weight on the hands and a good "white noise"-like sound.

Important tip: choose a bucket/container wih a lid, at least if you're as clumsy as me and wish to avoid rice everywhere. Also it helps keep the rice clean-ish.