According to the 1st post, its only impossible to join that room after he has joined another room..
On some servers (e.g. unreal) there are ban extensions.
The most common are
- ~q: quiet (+m for special users only)
- ~r: realname (banning the realname of a user)
- ~n: nickchange (people can't change nick without proper status, +v or higher)
- ~c: channel (banning everyone who is on the given channel)
I guess, ~r: and especially ~c: count as possibilities, too...