Toddler sleep help

We are currently in EST and will return to MST at the end of summer. Travel was rough on our 18 mo old LOs naps. He was sleeping 7-7 at home on mountain time which would be 9-9 here. No matter what we do, he is up at 5:00 AM, which is 3:00 AM in our home time zone. I don't want him to get his internal time clock used to that, but not sure what to do. We've put him to bed at 6; wakes up at 5. Let him take a longer nap and put him down at 7; still up at 5 so doing increments doesn't seem to be working. Any advice how we can nudge that wake up later?