The Arneson Model
The original Blackmoor campaign could be adapted for our use.
We would assign players a “role” at the beginning. Bob, you're the baron, your job is to keep the barony in the hands of the Earl. Jason, you're the village priest,you're job is keep the villagers safe and faithful. Marlon, you're the loner druid of the forest, your job is to keep the forest safe and pristine. Each might have a building or two, an income, and some troops/followers. We could even assign some people to play a bad guy faction, Toby, you're king of the orcs, your job is to bust things up. Or even raw up bad guy factions, give them to guys like Pete or Chuck to give us a plan of action.
Anything we'd come up for in the Gygax Model, would be needed here too.
I think this model might be better served by using some other game. OD&D/Chainmail, modified Pig Wars, It would be essentially a wargame with some RPG elements, so the characters would likely need to be simple and the ability to do mass combat important right from the beginning.
Whether the guys would really like doing that much mass combat is another question.