I've been racking my brain all day over this. Even after looking through the scripts in Reznod's Mannequins mod, I can't figure out how he gets the mannequins to hold their position even when the player is bumping into them. Anyone know anything about this?

I'm just guessing here, but maybe they don't have AI? Without an AI package, an NPC will just stand there and do nothing.

Without AI, NPCs dont move, but still look araound.

The manequins probably use the same functions as the player statue. A combination of:
setghost 1
setunconscious 1
setdestroyed 1
setav speed 0

Thanks QQuix. Turns out setAV speed 0 is what prevents you from being able to push an actor around. This is pretty fascinating to me as it suggests that when you push into an npc and they move, they are actually moving under their own power.