Vicar, first I want to join FP with the hope that your wife has a speedy recovery.
As for the wheelchair question, I think I'd look for someone who could fabricate some sort of "custom" trailer hitch to pull a very light weight trailer to haul the wheelchair and luggage as well.
There is a photo of someone who already has a trailer on the forum, so it can be done.
I think pulling a light weight trailer would be far more desirable than adding weight to the extreme rear of the car, which would effect the cars balance and its handling.
http://www.bushtec.com/images/reader...ike_resize.jpg