Sedatives would cause physical sleep, and the reason people share bodies in this world is because having your body be asleep will cause your soul to be eaten by insubstantial demons. Sleeping-while-someone-else-pilots-your-body is safe in large part because it cuts off interventions regarding your soul from outside sources - demons, drugs, magic, etc.
Also, this method relies on cooperative criminals, not just cooperative cohabitors-with-criminals. The criminal has an incentive to make being in jail really inconvenient for their cohabitor - by, for instance, not notifying anyone before going to sleep. They're already in jail, so making their cohabitor mad at them has limited power to make their situation worse, but if the guards wind up having to imprison the cohabitor too to be safe, the cohabitor might work on ways to get out.
I suppose reallocating cohabitors (say, criminals with criminals) is out of the question?
If it's worth saying, but not worth its own post, even in Discussion, it goes here.