Some county and state jail facilities will try to help inmates who are withdrawing. That may be in the form of giving methadone for the more serious addicts or giving clonidine, which is a blood pressure medication that helps with the symptoms. If his withdrawal is being treated, he has a choice. He could go to rehab or tell his doctor and get off the stuff, or he'll go right back to where he was. My money is on option 2.
I doubt there is anything you can do to stop him from continuing to abuse his meds. It's such a double-edged sword when an addict has legitimate pain that needs to be treated. Since you have no power over his actions, that leaves you with a choice yourself. Either stay and live with his behavior, or leave.
From this link, percocet withdrawals begin 6 - 8 hours after the last dose. It sounds like when he gets out he'll be maybe nearing the 24 hour mark.
Symptoms listed here.
http://www.addictionwithdrawal.com/percocet.htm