Self-bondage? Time to de-lurk.
I don't know if this is the kinda thing you mean, but I particularly like the "figure of eight" method. Take a length of string, about six inches long, and tie the ends together, making a loop. Put both hands through the loop and twist one hand in towards yourself. If the string is slack enough, the loop slides around your wrist, and you're back where you started, except your hands are bound together. You can repeat the twisting-in again, for tighter/stricter bondage; just as long as you don't panic & forget which way to *un* twist.

Three variations: multiple strands, for visual effect. If you're really adept, a much smaller loop works on the thumbs, either solo or in tandem with the above. Obviously, you can tie in front or behind the back; when I'm planning to tie in front, you can make it a little harder by using an elbow strap. I use a normal leather belt, set a couple of notches larger than my usual waist. It's quite easy to wriggle it up your arms, behind your back, 'til it sits just above your elbows. (I don't recommend lying down (YMMV).) Now just bond those wrists in front. The difference is, if you judge the relative lengths of the belt and string, your arms are *tightly* held into your sides, and you can't move your hands more than a few centimetres up and down. Ever tried to masturbate with your little fingers?

Two weird/advanced solo techniques: I once used one of those gravity swing devices; the kind you use if you have a bad back. You have a basic A-frame with a long flat board mounted in the middle. You stand against it and clamp your ankles between two foam-covered tubes (clunk, clunk - whoah, boy, not yet). Now you just lie back, and it all tips over, so you're hung upside down by just your ankles; with a few ropes and buckles, you could pay a lot of money for this kind of attention. Anyway, now you're there, you can masturbate and come in your own face - pretty humiliating. (Dominant mistress not supplied.)

Lastly, I once tried this; blindfold, gag, wrists behind back, short hobble on the ankles, but standing & otherwise naked. Gain erection (mental image of leather-clad mistress not supplied), then approach wardrobe. Place erection between doors, and rest the weight of one shoulder against the "outer" door. Clearly, although your hands are well out of trouble, you can get a long way with a semi-normal screwing motion, varying the pressure & torture aspects with your shoulder. Recommended, if you're experimenting with DIY dick-torture.