After doing a few searches I found that quite a few people like the Galco VHS :http://www.galcogunleather.com/vhs-shoulder-system_8_2_1334.html. I have a Galco OWB and can say their holsters are good quality. This one looks like it hangs loose and I can see that could cause a problem. Well the price is pretty steep as well.
There is this set up made just for wheelchairs: http://scotworksllc.com/concealedpouch.html Requires a separate holster.
A number of people like cross draw holsters IWB or OWB. I know sitting in a car this would work for me. Of course not sure you have the room in your seat and other factors involved. Massad Ayoob says cross draw is the best for wheelchairs. http://backwoodshome.com/blogs/MassadAyoob/2011/08/17/quick-handgun-access-for-the-wheelchair-bound/
The fanny pack made for a pistol http://coronadoleather.com/i-6785882-original-coronado-stealth-pac.html