Do the easiest thing first, which is to reverse kegel when approaching the PONR. When you're at the plateau, and this is where a lot of practice is required, you need to kegel hard for as many seconds as necessary to allow the orgasm to be suppressed. This is just damn hard. Your kegeling strength is vital. You will fail more times then you succeed at first. This is where you need a high-tolerance for frustration, as this is the part where most guys will probably give up trying to be MMO.
This could take months however, depends how often you practice. And do remember that practicing manually verses the real thing is not the same.
The progression after this get's easier. Once you're good at clamping your prostate (image your prostate is being squeezed by a vice-grip!) you can start controlling your orgasms better. You can try partially clamping down, i.e., clamping and then letting go again right at the end of the orgasm. In other words, start clamping at the same time you normally would to interrupt the orgasm, but then stop short of holding it as long as you normally would, this will allow a partial orgasm (which could be wet or dry). From this point more and more practice will start to teach you to read your reactions very closely. You can control (to some extent) when you have an orgasm, or you can ejaculate without having a full-orgasm, or you can let it build and build, holding off by kegeling for a while then reverse kegeling for a while, and have a more intense orgasm.
For me I can't imagine not being in control of my reactions, what I experience now is a world beyond what I used to do before. I feel now that I have adult orgasms (verses the 'teenage' ones I had before where I'd just explode and it would all be over). Don't know any other way to say it really.