I am going from memory here, but when you are in the game, can't you specify the team when you add the bot?
IIRC, when you are at the setup screen (say FFA), you can specify the number of players you want. Set all the slots to HUMAN. Now, start up the game. When it loads, of course you are the only one there. Now you can add the bots. Pause the game and select the add bot menu. I think here you can select the bot and specify the team. You can add as many bots as there are slots, which you specified earlier. Then once you unpause the game, off you go! I think this is one way to do it. Someone else may have a better way.
Hope that helps.