If you have carpal tunnel it is best to just give up the mice. It is the constant squeezing pressure you apply to grip the mouse that will give you problems. So switch to a Track ball, and not one with a tiny little marble for a ball. Find a track ball with a ball 2" in diameter or more.

The track ball that we use at work for anyone with carpal tunnel issues is a Expert Mouse from Kensington.

Multiboxing Everquest2 gave me Carpal tunnel. The PCB layout guy at work has carpal tunnel and recommended I switched to a track ball. I started using a track ball and don't have any more problems.
Well I should say I don't have any more problems with my hand, I still have lots of other problems.

Sorry the Expert Mouse only has 4 buttons and a scroll ring. But it will make your hand stop hurting.