Hey, maybe he needs his own forum? e.g. Billy Mayo (read/reply at your own risk).
i.e He can only post there. It would save everyone trouble.
I think "outside the box". Give him a Sticky note. "This thread is specifically for a member that has been banned in the past. We are trying a new idea here, by giving him a single thread/forum to post into. If you like the entertainment aspect, by all means post. If you don't place it on your ignore list. We think it's going to be a win-win for everybody. For fun, you could always place a "survey" in the thread. e.g. Thread survey. a) Has merit. b) No value at all etc.