This looks like a possibility. Gosher's -
http://www.goshers.com/blind-spot-de...ds3016-10.html
Here is some installer showing it off
[ame="https://www.youtube.com/watch?v=6joY5uMIA9k"]Goshers Blind Spot Detection System 2012 Toyota Prius - YouTube[/ame]
My problem is that I would have a hard time looking at those little circles cut into the vehicle. Even if it was paint matched.
I guess you can get away with just the rear sensors. They sell it in that config.
I would be more apt to opt for a side skirt solution if I wanted to do this.