Wow, yeah, it's certainly a "willing participant" thing. I had one Researcher that was originally intended to be a Breeder, but seemed to enjoy being at the research table more (women *huff*). So I just let her be set to Research and she wound up being the first Master all without coaxing.

I'd recommend trying to find one of the villagers that goes back to the table regardless of what you have them set to.

-Matt