There's no need to be greedy or selfish. Just polite. If he just says please and thank you, Alistair will get exactly what he wants.

Or what Cullen wants to give him; fortunate, really, that those two objectives align. But there's a small worry snaking through the back of his mind anyway: what if he stops, what if he says no, what if --

He tries to breathe through it. He'll take care of you. Trust him.

And that's all he has to think for a while. Mind blissfully blank, he turns himself over to whatever Cullen wants to do him.

(If that means they never make it back to their bed -- well, no big loss there.)