Dave, I wonder if 15" Fuchs (and 145 tires?) could be adapted to your chair.
The engineering seems pretty straight-forward. Wheel adapters and spacers could give the needed clearance for the lightweight Porsche wheels, and quick-release adapter-hubs could release
all of those components.. this would allow a quick switch back to the stock hubs, and an easy change back to the stock wheels.
Call me crazy, but...
~ Crazy Butt