"Crest"

 
Him learning to Crest is an optional enhancement to Devotional Sex.

Once this technique is learned he can Crest whenever she Wishes and he will keep Cresting until she asks him stop (going for too long gets exhausting).

When fully mastered, and with just a little mental preparation, he can even have a little Crest when he is not aroused or erect. This Wish can then be used at any time, and, as a little Crest is not too obvious, at any place.