A random chess position is given to the player. The position is winning for the players side and they are given a choice of two moves to make. They have X seconds to choose their move (X= 3,5,10? I don't know). The player feels they have a chance in this game because they have a 50/50 shot at guessing the move right -- and with a little bit of chess skill they should be able to pick a good move from a bad one, right?? But if you choose tricky enough positions, even good players won't do well in the short time limit.
You could make them play multi-move combinations if you want to make it harder. This game does bear some risk by the casino, it is 100% beatable since it is not a game of chance. However, this is what will draw patzers -- er, patrons -- to the game.
I think the Church of the Sub-genius is missing one of it's parishioners...