Set up virtual "stocks" representing a bunch of common words, phrases, or ideas he's likely (or unlikely) to say: for example, "evil", "terrorist/terrorism", "war", "economy", "crush the anti-americans" - or, on the opposite side of the spectrum, "antidisestablishmentarianism", "clean energy", and "free choice to all".
The moderator would have to record his speeches, go through, and find all instances of each phrase used. Each instance would pay out a specific amount, per share. For example, if you had ten shares of "evil" and a hundred shares of "crush the anti-americans", GWB saying "We must destroy the evil terrorists who threaten our lifestyle" would pay out 110 buzzbucks. Obviously someone with two hundred shares "terrorist/terrorism" would get 200 buzzbucks.
Of course, you could buy and sell shares at will - popular shares would increase in cost, unpopular shares would decrease. If you decided to corner the market in cheap "clean energy" shares and suddenly GWB got paid off by nuclear power activists, you'd make a killing - not only due to the payouts, but you could also sell your shares for a truly spectacular amount.
Even better, there's no reason we should limit this to GWB. Let it continue for all eternity, attaching itself to whoever's declared president at the time. Watch the economic turmoil the first time a third party is elected. Point and laugh when GWB's ratings drop and people start investing in "pro-choice" just to hedge their bets. You can invest in countries if you think we're likely to go to war with them (or, alternatively, ally with them/provide them with free food that may or may not be poisoned.)
I'd actually consider writing this up, but I don't know how to handle realistic stock-market calculations for small numbers of people . . . though I suppose I could just have buy/sell thresholds set, and let it balance itself through that.
It's a thought.