Unfortunately I can't think of anything you can use to block ad names. I will see if BbBoy can think of something when I speak with him tomorrow.
But for now it's fight them as they join, and it's worse if you have guest posting enabled like we have here in Tech Support just in case someone is having log in trouble or something they can post here as a guest. Do you have guest posting enabled anywhere? Also you can use the username-search the log and put that in the username input and see what IP# comes up. Report it here too and we'll ban it netowrk wide in the morning.