I have also modifed the game to prevent people from logging in multiple players at once from the same machine, because doing so is against the rules! If you have problems with the system seeing your home-network as a single machine, then try using the window client which is better at detecting your network configuration.
Update: Even if you can't use the windows client then up to 3 people on the same home-network can still play at once, as long as each player uses a different server.