That's interesting about the routine at the day nursery. DS (16mo) attends day care (same thing I assume) in Australia and the routine for toddlers (roughly 15mo to 2.5yrs) is morning tea at 9am, lunch at 11am, sleep 12 - 2pm, afternoon tea after they wake up. This would fit in with your routine a bit easier I think.
My advice would be to experiment a little. I agree with making his bedtime earlier gradually as he will need it with the earlier waking. I would then try putting him down at 12:30 without lunch (maybe with some milk instead) and see how that goes. If he doesn't go down or wakes up too early seemingly due to hunger, then I would try the half lunch before, half after idea. Even if this makes his naptime later, you might just have to do it. Or even give him a full lunch first. I guess it's going to come down to whether hunger or tiredness is the biggest problem at that time and also throughout the day. Certainly my experience is that DS won't sleep at all, or well, if he doesn't have food first, and even if he has his nap late and wakes late, he still goes to bed at night without any problem.
I hope it works out for you. Keep us posted.
Melanie.