So when you're mousing you hover your thumb over the pad? That's not tiring?
I click with the fingers doing the navigation, by simply raising and lowering them real fast.
If I'm clicking and dragging, I'll leave my pointer finger on the pad and raise and lower my thumb (it rests on the pad by default).
Don't get me wrong - I still much prefer a physical mouse, but if I have to use a touchpad I don't want to have to guess at where a button or scrollbar might be.