I have actually accomplished this a couple of times during sex. (Using the "Contract the PC muscles tightly method above)
The "full" orgasm I had after managing a "dry" orgasm was extremely intense - had me vibrating for hours afterwards
I must say though, it is extremely difficult to accomplish, and takes a mountain of both physical and mental control to pull off. I also have determined, at least for me, its not like this gives me hours of extra time. More like seconds, mabye minutes.
But honestly, if you can pull it off, IMHO it is worth it - and quite satisfying to be multi-orgasmic as a man. Just don't let it go at the dry orgasm. Finish off
Sammy