I was hunting around the "DIY Brake Ducts" thread and found this gem.
https://f87.bimmerpost.com/forums/sh...&postcount=163
It inspired me to try them on the rear of my M2 and, wow, it's pretty much a perfect fit! I think these will do nicely to stay on the rear with some minor trimming and zip ties. The rear brakes run far cooler on track than the front, so I am less inclined to trim brake shield at this point. I think just pumping some air into the cavity is going to be enough to keep things cooler and increase the service life of many components.