I'm certainly no expert but you didn't mention a third nap... is your lo still taking a catnap? My dd is almost 9 months and we only just dropped her catnap, but before we dropped it I would have the same thing as you sometimes and even now on 2 naps I'm having the same problem. Before we dropped the catnap, what I did was just get her up when she woke up early from the second nap, and yes she'd be cranky but then I'd get her down for a catnap maybe an hour and a half later and she'd sometimes get a good hour or more then. I didn't think we'd ever get rid of her catnap but somehow it seemed to work itself out... now I'm battling a short second nap in another post in this board
Now when she wakes early from the second nap I just get her up and then have an earlier bedtime, I don't know what else to do right now since I'm fiddling with the time I put her down for this nap. Hopefully we'll hit on the magic hour at some point and this will all work out for a while
Anyway for you I guess the question is whether he still takes a catnap and if not perhaps that's something you could add. If he is taking one then I can't help because I had the same problem as you and I never figured it out