Setting up an entity's bones before spawning

Is there some way to set up an entity’s bones before spawning it? What i’m trying to do is get a ragdoll to spawn with all its bones (including its physics bones) set in a certain position. Source comes built-in with a keyvalue for spawning ragdolls with a certain animation sequence, but this doesn’t seem to work in Garry’s Mod. I don’t want to loop through its physics bones after spawning it and set their positions because that method is very expensive and it only applies to physics bones. Anyone have any ideas?