I've only done it once with a toy (Orgasm + ejaculation), but I've done it maybe 5-6 times without anything (No touching, no toys, nothing at all other than porn and will power), and I've found a few things that you need to know / do.
1) Learn your body, before you even try to do this, learn how to control and then practice and strengthen your pelvic floor muscle. Just google 'pelvic floor men' without quotes and you'll find a few good resources.
2) If you pre-cum, make sure to practice doing these exercises in such a way that it feels good and makes you start to 'leak'. Once you do, you'll have found the right muscles to flex / move - keep it up and narrow down which muscles make you feel the best.
3) Go 2-3x longer than you usually do between masturbation sessions, it's important that you have the build up the first time you do this. It's much much easier and takes a lot less time.
4) Find porn that you enjoy, and is long. Or lots of it. Or better yet a partner who is patient and wants to try something new. I'm talking over an hour. This isn't something that's quick.
5) Get comfortable, relaxed, and worked up. It's important you're as aroused as possible before you start, so whatever works for you - do it. I find that going through my collection of porn for awhile without touching myself does it quite well.
6a) If you're going down the anal route, I don't have much info for you, sorry - the one time I managed to have an actual orgasm AND ejaculation at the same time (They're two separate things, more on this below), I did all of the above, practicing for a few months, flexed the muscles around my prostate and had a fairly strong vibrator pressed directly up again my prostate for about 20 minutes.
I've also had plenty of orgasms from anal toys (Usually multiple in one session), while leaking prostate fluids - which is also an amazing experience. For that I find that
Lucid Heart works wonders. Although any type of toy that is anal-safe, bent towards the prostate, and can provide some kind of stimulation towards it should work. It's important you experiment and figure out what works best for you. ScottA makes a good point in this regard.
6b) If you're going down my favorite route, the route that actually got me into anal toys - the truly hands free route, it's important you follow all of the information above, but set aside 2-3, maybe even 4 hours for the first time. Go as long as you possibly can without any sort of stimulation, and work yourself up . Be prepared to sit (Or lay) naked, with your arms at your side, for quite awhile, flexing various muscles 'down there' until you figure out what works best. Don't force it, just let it come (Pun intended). If you aren't feeling any sort of pleasure after an hour, stop and come back to it again later.
As for the orgasm-ejaculation being separate thing, it's odd but it's true - and even better, it's great for us. Why? Because we're able to have multiple orgasms, something that most people think is a uniquely female thing. This is something else you should practice if you really want to go after hands-free orgasms, learn to separate the two. One of the easiest ways is to learn how to control, and more importantly - relax all the muscles below your waist. Once you're positive you can, set aside an hour or two and
'palm the glans'. I started with this, and it's great to help you learn your body - something that's necessary when attempting a hands free orgasm.
On the other side of things, is to ejaculate without orgasm. Again, this is about learning your body, nothing else. To do it, merely get to the point of orgasm in whatever way you want, and right when you feel like you're about to ejaculate, loosen all your muscles. Do this until successful, or don't - it's not as important as the first one, but it actually helped me quite a bit because I was able to figure out what muscles I needed to tense to orgasm.
All that aside, I strongly suggest buying an Aneros, they subconsciously teach you everything I mentioned above and require patience. You probably won't ever ejaculate with one, but they can definitely bring on orgasms, and even orgasm 'waves' completely hands free, which is just as amazing. However keep in mind as with everything else, they take time and a lot of patience.
I hope all this was informative and not too terribly long. I've spent the past two years attempting hands-free orgasms, and my first truly hands free one took 6 months, my first anal hands free was after 9 months. Granted I didn't have the information I have now (Which I just gave to you -_^), but even with this information, it will most likely take you months to achieve, so don't worry if it doesn't happen your first try.
Also if you found this helpful, let me know - I've been thinking about putting together and ebook with all the information I've collected on the subject (Giving copious references to EF), but I want to make sure I've actually helped someone beforehand.
Edit: I just re-read my post and I wanted to make something clear. I have had countless hands-free orgasms from anal toys, however when I say orgasm in this regard I'm referring to just an orgasm, no ejaculation other than leaking pre-cum. It feels amazing but it sounds like this isn't what you want. It's great, different and sometimes better than an ejaculative-orgasm, something you should definitely aim for - but I went with the assumption that this isn't what you're after, so keep in mind that my post reflects this, and is about obtaining an ejaculative-orgasm.
If you're after -JUST- the orgasm, most of what I said is still true, however once you find the proper toy and have a relatively decent knowledge of your body (I.e. where exactly your prostate is, and what feels the best), you should be able to obtain your goal fairly quickly, within a few months. ScottA gives excellent advice for this.