No reference, but I read a detailed history of British aeronautical research in the 1930s. They experimented with perforated and foamed metal surfaces and rejected them for the reasons SoD stated.They settled for blown flaps.
To answer the question: I don't see piping under-hood air to the mirrors without increasing the frontal area. If you have a positive displacement cooling fan, or air brakes, you could pipe compressed air up the stem of the mirror and have Coanda nozzles around the mirror itself.
kach22i -- interesting thread