Indeed - and that's one of the reasons I mentioned round head tubes. Unfortunately there aren't too many easy ways to mount an ibike that don't interfere with the flow to some extent. I've considered some sort of aero-stalk extending above the rear of the saddle, or attached to the fork and sticking out towards the side, but I'm worried about the vibration issues.
Based on my dabblings in boundary-layer meteorology, I don't think the direction will be constant enough. I could well be mistaken, but my gut feel is that this would only work in some very special circumstances - like flat terrain with uniform surface roughness for considerable distance upstream and down.