The Two Pillow Mockup

First, get two fluffy pillows, approximately the same size. Place them side by side on (preferably) the bed. Position your erect penis in the crack between the pillows. Next, adjust the pillows to effectively create a "vagina": push the sides of the pillows toward your penis, and then roll the pillows' outer edges under you so your penis is up off the bed somewhat – this way when you thrust you won't hit the mattress. Now, reach under and adjust your penis so it's pointing downward at a slight angle (or however you prefer). Readjust the pillows for tightness, and pump away.