Winner takes all!

So, some people lastly made me nervous cause of leaving waaay before I defeated them, thus reducing exp I got. Would it be possible to "prolong" game so it would not end when there is only one player left, but when he decides to leave? Limit cap based on turns could take into consideration the turn when there was only one player left but that last player should be able to take all neutral teritories first to increase his exp even when enemy leaves.