Unfortunately, not really. I can take a guess at a direction for you, which would be to look in the conditions of an existing thrall spell, and see if you can change corpse for ash pile, either via drop box or by typing it in. If that doesn't work, though, I'm out of ideas. Ash piles and I...have a bit of a history. I managed to make a summonable "skeletal defender" once, using the corrupted shade body, but the ash piles were the one thing I couldn't work with. When the summon dissipated, the ash piles were there forever...and ever. When I looked into how to make the ash go away, I found that it was beyond my abilities, and there it has remained.