You will need a toilet paper (T.P.) roll (or paper towel roll), a broomstick, (or anything you can fasten the T.P. roll to, and not hit with your nads [ouch!]), a sandwich bag, some tape and some lube.
Use the tape to fasten the T.P. roll in the center of the broomstick, put the sandwich bag in the T.P. roll and wrap the ends of it around the outside of the T.P. roll, fill it with the lube. Insert your half-erect (or fully erect) cock in the roll (now kind of like a wet pussy), set the contraption on something about cock high. Grab onto the broomstick and thrust away.
(A word of advice: if the baggy is too short for your fully erect cock, or you thrust a little too hard, you will rip the baggy and get lube (then cum) in the T.P. roll, and you have to wait 'til you run out of T.P. again :( )