Hi
+1 for the tandem forum over at bikeforum.net. Very helpful.

Yes there is a tandem you can ride. The Co-motion Periscope is an ultra extending tandem to fit everyone, however you will have to watch out for 2nd hand ones on eBay, Craigslist etc as they are a bit expensive new.

Other options include getting a normal sized tandem and using crank shortners or kids crank entender to make the bike fit until he grows into it.

Folding tandems are pretty expensive for what you want to do and the ones you can by for $299 on eBay- well you get what you pay for!

Re hauling your tandem around. You can get roof racks that hold tandems, however we fit ours on our hitch on my car (Mazada 6) by turning the front wheel and strapping it and remembering that half a wheel overlaps on the other side. DH sometimes takes the tandem in his Hyunadi Getz on our strap on rack, but very carefully! If we travel long distance we take both wheels off, put a rear mech holder on and the bike is extactly the width of the car.

Firstly can you hire a tandem and give it a try with him? Riding a tandem is like driving a limo and does take trust and teamwork. For some people it works and some it doesn't. Also another way to give it a go would to be see if he still fits a Trail-a-bike and attach it to your bike. That way at least he can choose when he pedals and what gear he uses.