Starcraft - How to ally with AI in Custom Match?

It's fun and all playing a single random match against the computer but I want to know how I can ally with an AI and fight against another team of AI's. Don't mention "Go play online and ally with real people" or something gay like that. I went under game type to change it but this is all that is listed; Melee, Free For All & Map Settings. I'm pretty sure there is some way of making the map type 2 vs 2 or 4 vs 4 there's just got to be a way...