The ability to select someone as a diplomat. The job would kick in any time someone visits. If they are neutral they will try to increase your reputation with there faction. If they are friendly they will attempt to recruit some visitors to the colony, as well as increase your reputation. This would not happen very often. But you could add in some research options to build things that would increase there chance to raise rep and recruit. Things that you normally build to make your colony run functionally, morale and joy wise, would increase your chance as well. Basicly adding in another way to gain colony members.
Let me make this clear though. I don't think it should be easy. I think if you focused on it completely the whole game it would be a viable alternative to buying slaves but it would not be as reliable. They basically have to already be unhappy at there current colony before they would even think about joining you, and you would have to seem like a better option then there current situation. So in no way would it just be a passive increase to recruitment other then, slave buying, and capturing people who were trying to kill you.
Just a thought.
Let me make this clear though. I don't think it should be easy. I think if you focused on it completely the whole game it would be a viable alternative to buying slaves but it would not be as reliable. They basically have to already be unhappy at there current colony before they would even think about joining you, and you would have to seem like a better option then there current situation. So in no way would it just be a passive increase to recruitment other then, slave buying, and capturing people who were trying to kill you.
Just a thought.