Any way to set a different pop limit for each player/AI?

So I was thinking, "I think I want to recreate a battle between some gigantic empire (me) and several small AIs on a team." i.e. 300 v 100+100+100. I understand that the risk of getting swamped by raw numbers is what makes games like that interesting, but why not try scaling?

Is it possible to set different population limits in the normal game mode? Can it be done using Scenario editor? If so, how can some randomness be introduced between games? Is there a mod? Is it even possible to make a mod like that?

I'm more than willing to learn some modding skills, I just don't know if this kind of thing is possible. I've seen uncappers and house modifiers but that's not what I'm looking for.

Thanks all in advance.