I've often thought about this before, and have to agree with pspan. WTM isn't really about winning anything, except the respect of other players and the fame that comes with it, but what good is a group of players? I've always played here alone without any help (not even friends or family) and I like to think of my solving percentage (which is not that brilliant anyhow) as my own, always trying to enhance it. Nevertheless, I don't think there's any way to control that issue. If there is, however, I'd prefer to see a special Hall of Fame, or a seperate game, dedicated to group players.
Let people create groups. Make a group-ranking. That way, any solo-player can team up with any other solo-player. Maybe that will stop people making groups and pretending to be a solo player. If you implemented that, a while later you can built in that a user can't be logged in from two ip-addresses at the same time. That way you ennoy people that use 1 login for a group. I would limit any player to join only one group.
If you need extra people to code, maybe I can help.
"If you implemented that, a while later you can built in that a user can't be logged in from two ip-addresses at the same time. "
This would be very annoying, it would mean that if I still had a window open at home, because I am working on a particular difficult shot, I couldn't solve a few shots between classes at school.