I decided on Thursday that I don't actually use my right-thumb for any keys whilst typing, my left exclusively operates the space-bar, and there are no useful modifier keys on the right-hand side of a Microsoft Ergonomic 4000 Keyboard.
I decided to add something useful:
If you can't tell by the head, it's the remains of an xbox 360 controller:
This, combined with a modified version of mousex gives you an almost usable mouse.
Now I just need to train myself to use it.
As an aside, I used to be worried about damaging the wrist wrests and the other pieces of the body (both of which you can see mutilated above). I am no longer, they're almost indestructable. I had to switch from a craft knife to a stanley knife to get through the faux-leather on the wrist wrest.