For those interested, I've been doing a bit more research on this. A couple of sites have some good guidance on brake ducting:
How to Control Brake Temperature - Stock Car Racing Magazine
How To Install Brake Ducts
Airflow for us might a bit limited through the stock fang inlets. The real trick is delivering air to the center of the rotor. This surprisingly good InsideLine how-to has some good shots of the problem, although it doesn't show the side of the rotor I really want to see.
2009 Nissan 370Z: DIY Brake Pad and Rotor Change, Part 2
It seems to me there are three main challenges:
1. Routing - need to check what is between the bumper cover and the fender (can anyone else weigh in on this?)
2. Nozzle - I really like the nozzle the guy uses in the Zhome article above, but I'd have to figure out some fabrication.
3. Movement allowance for turning and suspension - this is what makes me a bit nervous. It's one thing to make a duct for a track car that only gets limited mileage, but designing a duct that can work safely for 10K miles or more is a bit tricky.
Anyway, suggestions/thoughts/comments welcome. I may try to embark on this in the next month or so if it seems workable.