Oh, yeah, there are TONS of topics like this up on the neuro board. You're right--cats are notoriously intolerant of wheels and tend to only like them for certain purposes of short duration, such as a change of position. With that said, that might be an idea for getting him off the spot. You're right--skin breakdown and UTIs (urinary tract infections) tend to be the biggest problems with spinal cord injury. Contractures are another possibility.
Personally, I used PVC to build a cart. It's cheap and light, but the hardest part was working out a harnessing system that worked. If you have access to borrowing some of those carts (wheelchairs) I would try some--different brands, sizes, etc. and see what works. Weight ain't nothing but a number.
You might consider a Drag Bag for some protection of the site. http://www.handicappedpets.com/walkin-drag-bag
Where is the spot? Knee? Foot? Other? A pic would be nice.