My ever shy Nat says that he's experienced "climax on demand" training for a male. But in order for it to work, he had to have a hardon in the first place.

From limp to orgasm - no.

From hard on to climax - yes.

His former owner was into denial and would keep his male slave(s) hard for hours...if they started to soften, he would have other slaves immediately tease them to an erection.

The "orgasm on demand" was acheived by giving permission for them to cum.