Yeah, empty bladder, empty bowels, deep sense of relaxation. It would probably help if he went a couple days without orgasm beforehand as well. Then just be patient. It might not happen the first, second, third times ...
Has he noticed a point where it feels REALLY GOOD deep inside him, like at the base of his penis but inside? That's where the good times are. You and he will need to find a way to hit that spot.