Matt,
If you want to spray it, you can safely do a side at a time. What I tend to do, is both sides at one time. But then, I also tend to hand-paint the the wheels a lot of the time... Anyways, hold it by the "sides", where the wheel will eventually go. Then you can use your wrist to rotate it. I the suspend it by by letting that little lip (once again, that part where the wheel will come over) - either by clamping it or simply by resting two sides of the wheel's lip onto something high enough.
If I said something in a way you don't understand and you want it clarified, just shout and I'll try another angle.
Do enjoy! Patience with the decals, please...