Oh I just thought of this.
I tried the ramp into the car idea. Didn't work. Give him a little time and he will do exactly what he was doing as far as jumping into the car before. Rocky, current tripod, jumps right in. Dennis, never did jump in. He would always put his front feet up (or foot up) and wait to be lifted in.
Our first tripod, Candy, was up and ready to roll the day after her surgery. She would still lap the other greyhounds in the back yard on three legs. I think she might have been faster on three legs.