15 inch small bolt Rallye Wheels???????

I never seen 15 inchers before. The basic plan is to get some rubber on the 7 inchers and stick them on the back of my car with the 14 inch rallyes up front. The only issue I see is getting some sort of trim rings to match the front ones even though the rears wont go all the way down to the base. Maybe eliminate the rings, put wheel opening trim on the car giving it an entire new look?
Chas.