I believe this situation is where the idea for the measles cue ball came from. After a few strikes to the side of the head, there should be a nice pattern starting to form on the cue ball. After he passes out, you automatically win by forfeit. Therefore, you collect your money, and leave him cab fare to get home.
Disclaimer.... I in no way condone violence of any sort in pool. Anyone who trys this tactic to win their match is on their own, and I will not be held responsible.
IMO... If I were running the tourney {or owned the room you were gambling in} and this was brought to my attention for a ruling, I'd have to ask any spectators for their opinion. {Providing he would not admit to it} If someone other than your best friend or brother said it was gonna hit the cluster, it's loss of game. And a warning to let the ball finish rolling at all times. If no one else saw what happened, I'd tell you to shoot the 6 in, and give him ball in hand and make him deal with the cluster. And he would still get one warning, before I sent him out the door.