Oh yes, it's very possible!!! And crazy fun!! I did it a few weeks ago at Horseshoe Valley in Ontario where I went sit skiing for the day. You will need assistance. Two snowboard instructors helped out me and my friend. One of the boarders offered to tow me around the tubing park in the inner tube and luckily, they had a sort of moving carpet thing that people stand on to get to the top of the tubing hills as opposed to people having to walk up (see photo--that's me in the pink boots, the guy in black is the super awesome board instructor who helped me out). I just sat in the inner tube, legs over the side, and he towed me around, got me on the carpet and kept me on it by placing his feet behind my tube, pulled me off the carpet, etc. We tubed as a group instead of all going one by one which is lots of fun. They were all complaining about how much it hurt their asses afterwards and I developed a pretty nasty bruise within a few days of doing it so yes, it's very hard on your ass/tailbone and next time I do it, I will pad the bottom of the tube where you sit, maybe with my chair cushion so as not to risk skin and tissue damage again. The tubing park manager made a HUGE deal out of me going tubing--he was very concerned with me hurting myself and I was getting really frustrated with him. Even the snowboard instructors started to insist that I'd be fine. I remained firm that I know my body and my abilities and he eventually backed off and let us do our thing. So if you encounter resistance from anyone saying that you guys cant go tubing, tell them to eff off and that yes, you definitely can. Ask them to keep your chair indoors if possible too. Usually they have some kind of booth or building in the vicinity. Also be aware of the risks involved--like I said, tubing is very hard on the butt, and like Steve Q mentioned, legs will be flopping around. I had one of the people I was tubing with accidentally crash into me and kind of crush my legs between our tubes because I couldn't get them out of the way. Luckily no damage done

You can get launched out of the tube easily or get airborne (which happened to me on one of our runs). It's definitely worth it and tons of fun though!!