Now I tend not to follow this form very much, so please excuse me if this has been suggested before. Still, I don't know that there's anyone else on this board who could actually carry out these threats.
If anyone accepts a pascals mugging style trade off with full knowledge of the problem, then I will slowly torture to death 3^^^^3 sentient minds. Or a suitably higher number if they include a higher (plausible, from my external viewpoint) number. Rest assured I can at least match their raw computing power from where I am. Good luck.
EDIT: I'm told that Eleizer proposed a similar solution over here, although more eloquently then I have.
So then your solution doesn't work. Any precommitment you make a mugger can just trivially overcome.
You're not following the process here. 'Which of you I believe more' is already being compensated for by additional increases in the promised reward.