
You can always give a medal to the winner and an extra medal for defeating the mapmaker.
I think that each map should have its own settings. For example, Research and Conquer will be best played with 6 players. So the "finale" would be for the 4 best players plus the 2 mapmakers.
Instead of making just one single game, you can make leagues with the most significant settings (spoils, reinforcements, FoW, etc) so the winner if the one who really owns the map in all settings (or most of them).