We could make a rule about not talking diplomacy outside the thread? It'll be hard to enforce, but...
We could recommend that people don't do it?
Permanent teams for whole games, like Bong-Mudkipz, (Darvince-Hamster)? (They would have to be balanced with equal numbers of players on each team, doesn't have to be teams of 2)
Then again, I'm not sure if it'd help much.
Rules to ensure balanced wars?