WheresWaldo .. have you ever considered a combined seatpost clamp / garmin mount? it would obviously need a little arm reaching up a bit for a device like the varia, and perhaps it would sit a tiny bit low, but it would be so clean! imagine that allez clamp flipped around, with the garmin mount projecting up from the closed/smooth side?

obviously it would have to be printed in aluminum or another metal, which is obviously expensive.