Bring the lights down and turn off the television or other screens when it's getting close to his normal bedtime, and when you want him up, open the curtains and let the light in. Also, if the weather is nice and you're able, take him outside. Light, especially natural light, has a big impact on circadian rhythm, and you can help him adjust faster if you make day vs. night lighting more dramatic. Given how late it stays light out at night, I recommend blackout curtains in the room where he sleeps. If he's able to sleep more restfully at night, and he gets plenty of sunlight during the day, in addition to sticking to his normal meal schedule, he should adjust in a few more days.
As far as napping in the daytime, let him have brief naps, but not full-on sleeps (if you can wake him without too much pain for either of you!). Like, 20-30 minutes. Then do something active and fun to get him up and going again.