[djshawk]

It may sound funky but I'd be tempted to push after he bets the river. I'm almost certain he doesn't have a 6, but may well have an ace so even though the chance is small he could possibly fold it for ~$300 more, unlikely I know but it's so unlikely you're behind it's got to be worth a shot.

Other alternative would be to shove the river, you had a hard time calling with an ace so he'd have a tougher time calling a full psb with one. Of course you don't get any value from him bluffing but you may take a pot that you would otherwise have split.