This I found out how to do by accident one day after getting out of the shower. I was in my room, not home alone actually, and went to reach for my boxers on my bed. I really wasn't in any rush to be clothed, but, I hadn't had a masturbation session in the shower, and was feeling a little horny. So, I got curious this day, and grabbed my pillow, and put it on the corner-end of my bed. I stood there at the corner-end, and slid my erect self in between the pillow, and the bed sheets. (Works very well with silk sheets, or very, very soft cottony ones..) Then, I started humping the bed as if I were in for doggy-style race. Whoa, was it amazing!
TIP: Make sure you have plenty of either socks, tissue, or toilet paper on hand. You'll need it!