I could add scalps the same way that I made the souls. The sideeffect is that every race would create scalps when they butcher a sapient being. I could make the scalps un-stockpileable, and make them rot away after 2 weeks into a "rotten scalp" and after 4 weeks they would be gone. This would mean that Dwarves have a few scalps in their butchery, which they dont need for anything, but Orcs could take them and use them in reactions.
I would only add scalps (elf scalp, human scalp, etc) to sapient races.
I would be ok with this. Orcs and Kobolds can take scalps, why not. Dwarves could just ignore them. And any race that can not butcher sapient beings (lets say elves or gnomes or humans, the friendly ones), would never get to see a scalp.