The only idea I came upon is to create hot seat game with 8 human players. Then pick 8 races that I want, and customize them to my liking. For e.g. I can create race similar to Ferengi by customizing Gnolams, or create something similar to Borg from Meklars.
After that I save the first turn. Then I edit the savegame, and I change 7 races from human to AI, and pick their behaviour in the game.
But it is boring to do this every time you start a new game, and also I am not sure will this editing corrupt the savegame.
So I was wondering could there be a way to force the game to select specific races when creating the new game?