[geoschmo]

Population is not the limiting factor here. There is a line in settings.txt that will allow you to make a mod with automatic population for new colonies. So you wouldn't even have to send a transport after with people on it. Unfortunatly it is impossible to colonize with a unit. You can give a unit the colonization ability, but you cannot give said unit the colonization order. The colonize button never lights up, and the units are ignored by the code in the planets screen when it's deciding how many colony ships you have available. So, your idea will not work.