My method

The very short description is that I do a tantra/taoism/kundalini yoga inspired routine whenever I am in the mood and have the time.

Executive Summary / TLDR:

• Breathe deep into the stomach
• Get somewhat aroused
• Use PC muscles
• Synch muscle tension and breathing
• Visualize "energy" up and down
  

The gritty details:

I meditate daily, even if it's just a few minutes, and I try to do at least some workout every day.

I take at least an hour for the whole routine.

I lay down, sometimes I lube up, and I get a bit aroused in the usual way.

Sometimes I stop the stroking altogether, not to avoid anything, but to feel the inner motions more strongly. I believe a lot of this has to do with focus, more than anything.

I avoid sexual imagery. It gets me over the edge fast, so I don't fantasize. Again, I think it's focus that matters most.

I focus on my breath, on my spine, on my prostate... I try to pull the focus away from the penis as much as I can, and into the whle body. One part of that is a visualisation of the chakras, which helps in guiding the focus.

I breathe deep into the stomach.

On the inhale, I clench the PC muscle. I also clench the inner thighs, like one does in orgasm.

On the exhale, I relax the PC muscle, and I pull the stomach in as if I wanted to push out all the air. I find that combination very intense.

This might seem like a complex, overly strict ruleset - I am not one for following rules too much, and I often switch around the combinations during a session. 

I change speeds, and I allow myself to be loud, moaning and groaning like in real sex. The vibration from the sounds somehow intensifies things even more.

I imagine the "orgasm energy" moving up the spine, mostly into my heart, and sometimes down again into the abdomen or even back into the genitals. I think those variations make very subtle differences, but it's not like one is more "correct".

Sometimes, when things get very intense, I completely clench my PC muscle for a while as hard as possible, or I kind of "vibrate" it, which I imagine is like a prostate massage of sorts.

At some point, I usually do a bit of "maha bandha", or "big draw" - I breathe in as deep and possible and just tense all muscles at once, and then let go with a big breath of air. This creates an incredible feeling, on top of all the awesomeness I already experience.

Well, and that's it. There are waves of intense pleasure, comparable to a "normal" orgasm, but still so different - all over the body, incredibly intense, and there's a long afterglow. At some point I just stop, often out of sheer exhaustion - or I decide to go over the edge and enjoy a good ole ejaculatory orgasm.

The most important part is not to expect a big "orgasm" that somehow ends it. It's more like orgasmic waves washing over me, again and again and again. It's a "the less you expect, the more you get" kind of deal. It's absolutely delicious.

The only downside is that there is no natural "endpoint", so I have to make a conscious decision to stop it, and that is really hard. But one cannot go on doing this all day, hehe, and by way of a little warning, there may be surprisingly sore muscles after that exercise! It's basically a stealth workout!