what a rude little boy!! haha joking hun, its very frustrating when u try all u can to settle them and they flat our refuse it!
perhaps one night put him down at 530pm when he's tired and deal with the early start and keep him up and put him down at his regular nap time in the morning, wake him up after an hour and a half(whatever his normal nap length is) then by the time his afternoon nap comes along, he'll either sleep for longer and then be awake longer of a night or u could wake him up again after his usual nap length and attempt a later afternoon nap. i dont know worth a shot anyway!!
good luck