I suppose you could deliberately invade an enemy province that is about to be attacked by rebels, and then keep your troops well back so the enemy and the rebels duke it out. Also, I think there is some trick that allows you to change factions midway through a campaign. I'm not sure about that so don't quote me on it. If it is possible, then you could deliberately provoke rebellions in your own provinces, switch to one of your enemy factions, and then do the invade-a-province-about-to-rebel thing. If you saved the game at the right time, you could do this again and again, and see different rebel forces each time.

Not quite what you asked for, but maybe close enough?