I would probably do the stick approach via something like a translucent overlay. I'm not sure the carrot approach makes sense to me personally because the rewards (no neck pain, etc.) are pretty intrinsic already.

I will definitely throw it up on github if I don't end up finding something else that already does it.

On a similar note, I have also been looking for something I could use to move my cursor between my monitors. I have a sort of a half-hexagon arrangement using 3 displays and it would be nice to be able to center the cursor on whatever one I am looking at.

I think there are applications out there that sort of do this, though, so I am hoping I luck out.