Such a sick little touch. I love it.
One of my buddies Chris Gonazales is a tinkerer. He owns a tracked out S550 and knows his way round an LED board. He developed some custom rear LED lights to replace the reflectors in the S550 rear valence. Pretty slick when I saw them for the first time, and asked him to build me a set. As far as I know these were the first set to be installed on a car that wasn't his.
The install process took me about 3 hours, but it was because I was being a dunce. The rear valence on the GT350 has some added bracing in the way of removing the one nut that bolts the reflector in place. Once I figured out I could push things around to get my swivel in place the removal was pretty easy. Chris wrote up some instructions based on my experience, and even added heat wrap to block the wires from the exhaust. The only thing you need to remove on the GT350 is the lower diffuser, but that comes off easy enougt.
Here is a short video of them in operation. They work as a running light, brake light, turn signal, and hazard. You can also disconnect certain wires to make them work how you want.