This is clean and simple. Kneel facing your bed (or a low chair or something like that), and lean your upper body on it. Prop up whatever you like to look at on the bed in front of you, and masturbate. When you go off, your body is free to thrust forwards, and your balls aren't bunched up between your thighs and your hands like if you're lying on your back. It feels great-gives some of the best orgasms I've had outside of a bath.
It can get uncomfortable pretty quickly if the bed or whatever isn't at a good height or you can't find a good position, so this might be best for quick relief rather than a prolonged session.