I'm pondering using a mook rule where any hit that does more than 5 + the mook's Fort save bonus takes the mook out. What I'm really trying to do is reverse-engineer the massive damage save with the presumption that the mooks will roll 10 on average (sort of like static AC) on the damage save. There's got to be a way to allow the mooks to stay up & in the fight until a certain hit just takes them out of play. Then, the main foes can have hit points to track just like usual. Of course, the PCs track their hit points, too.
Sorry about that! I wish I could say I was ahead of my time, but its not true.