Take him for a long, long walk in the morning. Not just around the small patch of grass, but go for an hour long walk with him as soon as you get up. Chances are he'll have to go at some point, walking does get things moving. When you get home, do the same thing, long long walk. Eventually he'll get used to the routine. If you can get a dogwalker to come in at noon, that would be a good idea too, same thing, nice long walk. Boys like to pee to mark their place so the more places he gets to sniff..... you get the idea.