Steve,
Reading your post reminded me of another poster on a digital photography forum which I try to browse every now and again. His name is Stuart Rider. Here is a link to a thread he started a few years back with regard to the ChampCars at Brands....
http://forums.dpreview.com/forums/re...essage=5045816
(read through, - he makes reference to his circumstances).
Here is his pbase gallery...
http://www.pbase.com/srider
It looks as though he mightn`t be shooting that much motorsport recently, however he could be worth contacting. I remember seeing him at Brands a few years back (well, I assume it was him) and was really quite impressed by his results given his disabilities and the way he was having to shoot.