Comparing cutting edge race cars to street cars never works out well...
I see some promise in injecting the additional air around the perimeter of the tail end of the car but it also makes the ducting much more complicated than just dumping it out the back where it's convenient.
I have a very simple, inexpensive, and reliable piece of technology which routes all the air and a lot of the waste heat from the engine to a point at the rear where it helps 'fill in' the wake.