I think you are missing my point.
Say the Bannor send some settlers to another continent (a requirement for liberating a colony) and found some cities. Perhaps these islands were not uninhabited, but there were some small tribes of orcs who hadn't built cities or even villages yet. The Bannor put them to work, and the orcs, more numerous than the Bannor, represent a sizable amount of the population. When the Bannor decide that administering this colony is too costly, they put these Orcs, whom they have civilized, in control of themselves, like happened in the real world.
Maybe the Orcs keeps some elements of the Bannor culture (i.e., if they spread the religion there before liberating), maybe not.
Another way to do it, but wouldn't be as fun, imo, would be to create another Bannor civilization, led by a random leader, ala unrestricted leaders option.