I assume you were playing some bastardized rules with no safes?
Because if safes were allowed, Im thinning the 8ball into the 1 and leaving it behind the other two balls there with the cue ball at the rail.
My first thought exactly. Make him shoot the low percentage shot and break those other balls out. The only downside is that he will likely just play you safe back and you will be in a world of hurt; especially if you are playing ball in hand.