You can create a modified Version of the .map file adding in AI's and also adding special boosts for them such as alliances with each other, extra units, even fully design their gods.
You can select 5 or 6 races at the selection screen then when the game starts you can turn them over to the computer AI.
It might work for you to create gods for the ones you want to be AI and copy them to the game directory. Im not sure how you would start a multiplayer game and have the computer make gods for the AI's. but I am curious now so I might hack on it abit to find out.
