I like this idea for a mod. I think the idea about using the whole map is also fine. Now, in order to keep to the spirit of Col, I wonder if it would not make sense - game-wise, that is, not historically, of course - to assign each particular colonizing civ to a homeland far-far-away in the East, that would not show on the map, like in the positions occupied by China, India, Khmer, and so on but with different names.
Why not have as "Europe" a bunch of things called "Proto-Greece", "Proto-Egypt" or something like that?
Just my 2 cents.