This car was able to have painted stock wheels during the 2.0 update. I know 'cos I painted several different versions of it. When I updated GT5 past the 2.0 update, all the G37's I created were unavailable in my garage. I had to remove them from the garage (had that "need to download car again" message). I have been tempted to roll GT5 back again and see if I can get this one to work, but it's too time consuming, and I don't want to risk losing anything.
I had painted the wheels on this one in chrome, metallic silver, same chip from the car, matte black, metallic black, etc. I had close to $20M in my account when I did this, so I went crazy with all the cars that could get stock painted wheels. The only ones that I was able to keep when it was all said and done were a few of the Maserati's.
Good luck finding this one.