The only thing I would say is that when a child wakes after 9-10 hours sleep, it's typically a sign of being OT. My son does this on occasion, and it's always because he either a) had a short nap during the day, b) went to bad too late, or c) is teething.
I think part of the problem might be that you let him treat that waking as the beginning of his day. Have you tried soothing back to sleep? When my son does his OT early waking, he totally sounds awake! He wakes up chatting and playing. We've done enough sleep training at this point where 50% of the time he'll go back to sleep on his own. If he doesn't (and starts crying), then I go in, give him some warm milk, and cuddle him for about 10-15 minutes. At that point, I put him back in his crib and say "It''s night-night time! Mama loves you!" and leave the room, whether he's asleep or not. He always falls asleep on his own at that point.
You might also try the wake-to-sleep method, since it sounds like you've got an habitual waking at this point.
Basically, I think you've got 3 options:
1) Work on figuring out why he's overtired. Does he need to go to bed 30 minutes earlier? (i know you're already scared hearing that, b/c your wakings are so early already!) But if it IS overtired, an earlier bedtime may battle the OT problem, and get your son to have a more normal 11-12 hour night.
2) Treat that EW as a NW, and do whatever techniques work to get him back to sleep.
3) Try the WTS method so that you can break the habitual waking problem.
Since it's been going on so long, I'd be inclined to try methods 1 or 3. Experiment with the OT problem and just TRY an earlier bedtime for 1 week. Worst case scenario, you're in the same situation you're in now. You could also get EARLIER wakings -- a 4 am waking may feel more like a NW to both of you, and then you can treat accordingly rather than be tempted to just start your day. Heck, my son has had EWs at 6 am because of being OT (went to bed WAY to late at 8:30, or something like that). I still treated as a NW and let him sleep until 8 am!
Method 3 might work as well -- WTS is where you go in an hour before your child habitually wakes, and just gently touch them -- your goal is to get them to just stir in their sleep, not wake up. You want them to move their head or body ro something mild like that. The hope is that this will re-set their sleep clock and you'll change their sleep pattern.
I hope that works! It truly sounds like OT to me -- that's just too little night sleep. An early bedtime would be a great way to start, as scary as that sounds! (I got similar advice during the 2-1 nap transition -to wake him early from his 1st nap - and it nearly killed me to try it. Thank goodness I did, because it made the transition SO much easier!
).
Good luck!