How about a tag-up rule where the player that's offside, assuming it's by a marginal amount, has to go back and re-enter the zone? If he doesn't within, say, 3 seconds, offside is called. If he involves himself in the play in any way before tagging up (or before the 3 seconds have elapsed), intentional offside is called.
At this point, the question becomes how to effectively communicate to a player that he must tag up. In theory, having the linesman yell "Number 16, tag!!" would suffice (we all know that linesmen can scream), but is that effective when the crowd is really raucous? What happens if the referee is too busy jumping out of the way of a player (or getting knocked around) to call out? Or would it just be the player's responsibility to know he's offside and react accordingly?