If you want him to sleep until 6.30 I'd leave him to nap long and tuck him in later, he will eventually wake later, it will just take a few weeks for it to settle. Then the tuck in for nap will be later eventually, too, may take a couple of weeks though. Not getting him up or make any action before 6.30 is a good idea, he will eventually understand that it's still bedtime...
It does work, just takes long, you know what I mean... Is it possible to make nap time 12, no matter when he wakes up, so that his rhythm doesn't get used to the early waking?
BTW, it's not that out of synch, look at the 4 am wakings of some toddlers...