If I'm not completely off, I think that it is the player that is closest to the basket that goes for the alley-oop whenever it is called.
You could combine the Off-Ball control with the alley-oop though. That would be the best way to go about it...

So just take control over which ever player that you want to throw it down with, and try to get open, and then hit the alley-oop button. The player always goes for the alley-oop, as long as you’re within dunking distance, although it's not that often that he completes it if you play on a high level of difficulty since other defenders tend to help out by disturbing you.