I hadn't heard (well, read) about anyone doing this, so I thought I'd pass it along.
One fun way to masturbate that I used to use with some frequency some years ago was to 'have sex' with an old sleeping bag I had. I'd have it rolled up as tight as I could for storage, and what I'd do was simply take a plastic shirt bag (they are long and so stay put inside the sleeping bag roll) from the cleaners and put it inside the center of the rolled-up sleeping bag. Then I'd put some lube, lotion, hair conditioner, KY, inside the plastic bag and-instant sex toy. I'd usually get it on with the sleeping bag on the couch, which offered a variety of positions from missionary style, to doggy while kneeling on the floor, laying on my side, whatever. The inside of the bag was slick and fairly tight, and it was very comfortable to hump (which isn't always true of some other quick home-made sex toys, like a bag and lube betweeen the mattresses or couch cushions.) One of the nicest thngs was the sleeping bag actually gave me something to hug and really hold on to while I humped it. Definitely worth a try if you like to hump things and are looking for something a little different.