Do you remember that scene in the Dark Crystal movie where the podling has his life essence drained away and left as a broken slave.
For those of us who are sorcerers we should have an arcane station as an alternative to the wheel of pain. Where we strap a victim into a chair facing a chunk of Blood Crystal. We should see a red light draining their willpower away. Once they are done they should look fully corrupted and work as any other slave.