Here's an idea. How about running a scenario where the PC's are the folks whose homes are being invaded? The Orcs from TOEE for example? Having survived the initial onslaught of the more powerful PC's (by running away or playing dead), they are now stuck inside the temple. Either they can't get out, or going outside is instant death, as in the TOEE is surrounded. They must survive within the Temple, as Home Invasion Group (normally the role played by PC's) continues their onslaught. There could even be multiple groups of PC's invading at the same time.
The Orcs would have to be more clever than their kin, and their goal wouldn't necessarily have to be to kill the PC's, as much as it would be to get the PC's killed or otherwise defeated, while the Orcs navigated the dangers of the Temple themselves. Level by level they would be pushed down, and would have to manipulate the tricks, traps, and inhabitants of the Temple into defeating the PC's. Along the way they may find out the secrets of the Temple itself, like the Elemental Nodes, etc, and use that knowledge for their own benefit.
Definitely a roleplay heavy venture, where player skill is all important. More than likely the Orcs wouldn't be rewarded or recognized for their efforts, just surviving would be the goal and reward. If they managed to scavenge some loot along the way from fallen PC's or evil guys, so much the better.
If you want to give a little bit of xp to the Orcs, that would be fine, but not enough to get more than one level. The Orcs definitely should not progress in level enough to ever be able to challenge the PC group. Hence, the PC's would get relatively stronger and stronger as the adventure went on, and the Orcs would have to get smarter and smarter to make survive. Meaning, the players have to bring their A game.
This sort of turns the typical adventure on its head. I think it would be fun as hell to trick the players into it. They show up, character sheets in hand, expecting to play the adventure normally, and then you get to use their beloved characters against them. Any backup characters they bring could be used to make the second or third adventuring groups.
Damn. I just started typing this idea out as the thoughts came into my head, stream of consciousness style, as I wait for the pizza guy to get here. But the more I think about it, the more I want to do it.
I'm going to bust out the TOEE book....