Krissy,
I don't know what your day care situation is going to be, but I've heard and seen that many LO go to 1 nap very early when they are in a daycare situation because that's how the day care tends to be set up?? A lot of daycare centers only offer 1 nap after LO transfer out of the baby room? Do you know where your LO will be going yet? Maybe you should talk to them and see.
If you can't get him onto one nap by that time I'm sure the transition will happen soon after you start and then it will just be a bumpy few weeks until he adjusts. You might have to offer a small catnap or something like that some afternoons, or he might just make the jump without a bit to-do.