Sorry I missed this, was OOT for the weekend. Unfortunately, I don't know that I have lots of inspiring advice.
The only thing is, if you're doing a 6:30/45 pm bedtime, 6:15 am isn't really considered an EW. He's still getting 11.5+ hrs of sleep. But, I know it's hard to then get to the one nap with the earlier wake. It's such a hard spot to be in.
I think staying with one nap and getting it to lenghten appropriately is your best bet. Otherwise, you're going to have to push that first morning A out for the CN (probably to about 4 hrs), but then that starts to mess with the rest of the day. Is your DD done with school now? If so, I might be inclined to just stick to a set nap time (of about 12 pm), and adjust bedtime accordingly depending on the nap (6:30 ish for a shorter nap, and 7/7:15 for a longer one). How does that sound?