From what I've read, the Dream moments are all random, and computer-generated. The computer will say "at x time be at x location, and the first x people get x".

Or they will be directed to the exit from Maliboomer at a certain time, so anyone exiting the ride will get dream ears or something like that.
On the other hand, there are people who give out Magical Moments, and we got one of those (special seating at a Billy and the Hillbillies show) because we smiled at a CM and said hi to her. But for an actual Dream, that's not supposed to work, and in fact people have tried, but if they haven't been directed to give something out at that time, they can't.