There is a sound medieval precedent in the electors of the Holy Roman Empire(
http://en.wikipedia.org/wiki/Prince-elector). Each realm could elect their electors, then the electors elect the Emperor. The Emperor's position as a game mechanic is tricky though he/she would have to maintain the empire through politics. It seems doable though.
As long as each realm gets an equal representation in Electors, with the tie breaking vote given to the emperor. It should be fair enough.
