Coming in in the middle, but...
Why not use some kind of illumintation at the prop tip, so that at night the movement of the light traces an arc in the sky? This would show a large circle where the prop was spinning, as opposed to two/three/four points of light when the prop is stationary. Obviously this would only work at night, apart from really bright lights, and actually illuminating the tip could be difficult structurally (fibre optics?), but it could be a solution...
-tacc
[This message has been edited by Teenyweeny ATC Cdt Cpl (edited 09 April 2001).]