I think what's probably the ideal way to handle this is to have a semi-circular section of LEDs (or a darker plastic panel that will conduct light) that appears very dark when unlit. When driving in regular conditions, a parking light of sorts set behind the LEDs would be lit, creating the afterburner effect. Then, when you hit the brakes, the LEDs light up and that's that.
Despite the idea seeming relatively simple, I have NO idea how difficult it would be to implement. Just thought I'd share my thought.
3/13/09 - Ordered Aqua Blue Metallic 2SS/RS M6!
7/13/09 - Built!
8/11/09 - Delivered!