Here is how I resolved the issue for my bug. I haven't tried it yet, but i believe it will work as the scoop are located in a high pressure area (front of rear fender) compare with side window mounting. Anyway I don't think it a big deal as the NACA duct has a foil effect trapping side moving air.
Check my solution here:
http://www.germanlook.com/Forums/showthread.php?t=8207
Louis