I did it accidentally the first time when I didn't want to cum at the time during lovemaking. After that, I knew it could be done, so I could do it.
The best I can describe, get as close to the edge as you can then clench (what I meant by clamping) your PC muscle, and breath deeply and slowly. If you time it right, you will get an abbreviate set of orgasmic contractions and euphoria, but you will not actually ejaculate. At least that's how it works for me. Timing it just right is the hard part, and maybe it doesn't work for everyone. Give it a try and good luck.