In fact I almost implemented the ability to place multiple initial populations. Though I didn't complete it because I want to wait to do an editor focused update. My goal with that update will be to allow full mid-game editing. So you will be able to stop the simulation at any point and do things like adding/removing groups, change cultures, add discoveries, and even customize polities. Of course I have no idea when I'll get to work on that : /
Don't worry. You can always play around with the game mod files and add mods of your own. That's a way of cooperating too :)