[Zetack]

As other people have said, you win with it, you win with it. If it only counts when its a bluff you might as well eliminate the 7-2 part of it altogether and just pay off any time somebody wins a hand with a bluff.

1.5 BB's I think is a good number. Its small enough (one BB and on SB) that it shouldn't bother anybody to pay, but if you're playing nine handed, it gives you 12 BB's to play for with your 7-2 thus giving a pretty good incentive to play the hammer. Somebody mentioned 5 BB's, which would make for a really wild game, with a 40 BB payoff, plus the pot, people would push the hell out of their 7-2 hands, but after the fourth or fith time you pay out 5 BB's to a 7-2 hand I think you're going to start getting annoyed at the hit to your stack. So, 1.5, or 2 BB's max, I think are the ideal numbers.

--Zetack

Edit: you'll need to decide what to do in a side pot situation, where the 7-2 takes the side pot and loses the main pot to the all-in player.