I've been messing around with the same idea and I'm having the same issue with deciding where/how to mount it with my CA plate (required by law). I mean, I now plenty of people who don't have any front plates (myself included on my old truck) and have never gotten a ticket for it. However, with my luck, the first day I have it on the car I would get one. I've tried mounting it in the windshield on the passenger side pillar (vertical style) and that created a bind-spot that I wasn't comfortable with. But yea... I'm open for alternate ideas.
Also, I ordered one from
http://www.customeuropeanplates.com it wasn't too expensive IMO ($45). Took about 3 weeks to get here (custom made in and shipped from Germany) and came with mounting hardware/frame free. I'm sure there are other sites as well... But I am not known for shopping around too much after I find something I like for a price that I think is not too bad.
