If the professionals haven't warned against it, I would suggest that a hands-on or oral approach would probably be safest. Keeping his movement restricted and another person's weight off of him are probably the best things to do, though I'm in no way a medical professional, so I'm just guessing here. There are many ways to show affection and give pleasure without penetration.

If he's not adverse to "toys" you might look into getting one of the masturbators fashioned after a porn star. It's not the real thing but he could still have the tightness of a pussy/ass but not the weight of an actual person on him.

a swing?

... about sex for people with physical challenges.

The main thing is to start from what he can do (without hurting himself) and work the sex into that set of constraints. I'm not going to guess about your friend's condition, but there are many biomechanical strategies for coping. He may need mainly to readjust his ideas about how to have sex (like forgetting about the missionary position, for example.)

It sounds like you need to hunt around for a good physiatrist (NOT psychiatrist!) who's comfortable with sexual issues. I'd start by phoning the San Francisco Sex Info hotline and seeing what they have for referrals. Don't expect someone to work this out over the phone or on the internet; you really need to find someone who's an expert in rehabilitation therapy and work with them. Some of these people are pretty sex-negative, but many are not; it's coming to be recognized as an essential part of the practice.

Thanks for all your ideas. I had thought of a swing and also a company that puts out Love Furniture. A lot of that looks promising. It's made out of carved dense foam so it's supportive but not hard. In fact I just found something called a Love Rocker. It all looks interesting. We will definitely be looking toward movement specialists. Kinda sucks that water is out for sex and the parabola plane is booked with astronauts but we'll deal.

www.loverocker.com/

www.theooh.com/intimacy/item.php

either one would take pressure off his back.