This technique lets you use your hand in a way that more realistically imitates a vagina. First, lube up the palm of your hand of choice. I'm going to assume this is your right hand—for lefties, just reverse all of the following instructions.

Lie down on your left hand side, on your bed. Take your right hand and grab your penis with the Reverse Grip, so that the back of your hand is facing you and your thumb is near the base of your penis. Now roll over onto your stomach so that your hand is trapped beneath you. Rather than moving your hand, begin moving your hips up and down like you would during intercourse. It should feel much closer to the sensation you'd get if your penis was moving in and out of a vagina, and the thrusting motion of your hips makes for a completely different experience than if you were just moving your hands.

Instead of the typical stroking motion, simply tap the front of your penis lightly and repeatedly. Move up and down, focusing mostly on the spot most likely to bring you to orgasm. It may not be the most satisfying experience during the initial stages, but the intermittent pressure has potential to help you build to a pretty dramatic orgasm.