There are a number of devices that are designed to help with rsi.
The device your gp is thinking of is prob. the trackball, this is a kind of upside down mouse, which you use with your thumb.
You may like to try using a graphics tablet, where the stylus is used rather than a mouse and feels like using a pen. Not just for drawing or paint progs.
Theres also speech recognition software, nowadays this is much improved.
This site takes you to a page showing the Logitech family of Trackballs, has some pics so you can see what they look like. click here
I suggest that you go to a large pc store and try out the diff styles to see if any suit you.
Also, google rsi, tracball, etc. to get more info on the subject (I just did and there's loads).
Hope this helps.