I'm trying to make NPCs walk through each other, but haven't found a way yet. Granting them (and enabling) the privilege "freemove" doesn't seem to have any effect.

Besides writing a pushthrough hook is there any simple way to make them ignore each other?

You could try to set stamina to the maximum at each move.
But imho NPCs will not step on each other even if you do that. So neither setting freemove or setting stamina to max should work. That's at least my experience.