but if it stands, I would consider your son not finding a replacement. Say it's a 6 man apartment, if he can get each of the other 5 to chip in a couple bucks, your son might get below the 85% he would have to pay anyway.

The other 5 have an incentive b/c they can have one less roommate taking up space in the apartment. Ask 4 guys to pay a little and the one who'll end up with a private room to pay extra and your son just stays on the lease.