Alright so a few basic things first off.
Creating a character simply to stonewall another player is not a permanent solution in my mind and can lead to out of game fighting or arguments it comes to light that you're intentionally preventing him from the play style he appears to have the most fun with. That's not condoning his behavior, just a warning of something that can come up.
Before starting Kingmaker, I would recommend the GM and Players sit down and discuss out of game what kind of kingdom they want to build - and who plans to take on what role within it.
This would allow everyone to have a general idea of what to expect once the kingdom building rules start coming into play.
There are also rules for different forms of governmental rule such as Oligarchy (which is what my current game is using), Theocracy, and a few others.
Oligarchy gives every member of the "ruling council" a domain within the kingdom so there is not one absolute ruler.
Just a few quick thoughts.