I suggest you pick up a powerball www.powerball.co.uk

it did me a world of good, and they're ace to play with too!

There are excercises you can do to build up strength into your wrist and hands.

http://holistic-online.com/Remedies/...-exercises.htm

HOWERVER... I AM NOT A DOCTOR, and whilst I had RSI, it was NOT carpal tunnel.
With this advice, your milage may vary. Speak to your doctor before using a powerball or doint the exercises as it may aggravate the issue.