It is interesting, that when one relaxes enough they can hold back longer. If you were working with someone to be able to hold a release longer that is what you would do. On the other hand, when they are fighting not to release, the muscles tense, and the resultant release is even more intense. So how do you do that?

One way to do it is to make it initially a game, showing him you will stop immediately when he says he is close, he will test you and not go all the way to the edge, but watch out he may not know himself. If you promise a great release if he holds it till you say ok, it provides the initial incentive. Then along the way you make mention of things like post orgasm torment with an early release. The first time he hears it is not that important, the second time he is on edge so much sooner.

by the way there was a lady that has retired that did nothing but extended edging and milking named Sultry Sadie. She used restraints and CBT to extend a session. she has written two books on it, on amazon under her name. The first is named sessions. very detailed.