in regards to your second link... i would not recommend...it has piss poor reception and the mousepad is not i would call quality, it has tracking issues for sure.

Honestly a Apple Trackpad might not be a bad idea. Just turn sensitivity up so he doesn't have to move his hand very much.

Does it absolutely HAVE to be a trackball? If a D-pad+software could be better, I could maybe build it out of a USB NES controller. I've already made one just for the sake of doing it, so it would be a piece of cake to make another shell to fit his hand. I know that's wired, but IIRC you can get adapters that can let you use USB stuff remotely (USB->adapter->goes through air->other adapter->USB port on computer).

I just found this too, would that work?