Forget him, ask me, I love it!
Actually, just try in the shower. After you let him see you soap your ass clean, bend over and have him go down on you from behind, then, using the fact that you're turned on by his excellent performance as a cover, quietly whisper "lick my asshole baby." Most guys want to be the king in bed for their girl so bad that if he thinks he has you loosing control he'll do whatever you want to push you over the edge and have you screaming about how great he is - both to him and your girlfriends (this doesn't have to be true, but it's what he'll feel is true).
Good lick ;)