On an average day Meta gets 4 or 5 cross posted questions from question banned users on SO. How about a review queue for incoming questions from q-banned users?
All questions from QB users could be redirected into a queue temporarily (say 15 minutes), during which time if the question gets enough off-topic delete votes* it never makes it to Meta. If the question doesn't get enough delete votes (either because it is not off topic or because no one is looking at the queue) the question will show up with the rest of the normal questions.
What do you think?
*We would only be judging on topic-ness here, not quality.