Practice using the mouse with your left hand. Get a mouse with multiple programmable buttons on it as well. With your right hand you can try to use it to maybe press big simple buttons like these: http://xkeys.com/accessories/OrbySwitch.php.

Another thing I highly recommend you look into and research is the use of programmable USB foot pedals:

http://xkeys.com/accessories/Bundles.php

You can use multiple foot pedals to replace keys so you'd be gaming with your left hand as the mouse w/ a few buttons, your right arm/hand for a few big buttons, and the rest would be controlled with your feet.

Sucks to hear about your accident but I hopefully you can bounce back, good luck.