I think if you have all of the windows down (rather then just the front 2), you promote laminar flow of the air rather then turbulent flow. Although it is still not as smooth as air flowing over closed windows, it will smooth things out enough.
I only use the AC when its raining or when I absolutely need to use the cell phone (w/ear-piece)... even then, I try to cycle between the AC and the vent. The compressor seems to rob a whole bunch of power, and I hate the surging/bogging feeling that it gives the engine (especially mid-shift).
