Well, I suppose you could mount the wheels just on one side of the car. People generally only see one side at a time and most will never know the other side has different wheels.
My brother did that years ago when he couldn't afford to buy four "Mag" wheels for his Camaro. He thought putting two wheels on the back axel would'nt look right since front and rears didn't match. His solution was to put them on one side so the wheels matched side to side.