Sleep ins needed

Any suggestions on how to train an almost 18 month old to sleep in? He’s shattered at night by 6pm but even forcing him to stay up til 7pm still generally means a 5-5.30am wakeup. It’s driving me stark staring BONKERS!
He sleeps pretty well at night, but the early starts are killing me. I refuse to get up to him until at least 6am, but of course once I’m awake I’m awake, so this doesn’t actually help the amount of sleep I get. Suggestions most welcome!