This is just an inventive guess on my part. Take a light source (flash light or electric light) cover it with an opaque white covering (similar to that seen on some ceiling light fixtures?), apply a layer of the stick-um and wait for the cluster flies. They are attracted to light and to light colors, so this should work.
[and yes, I just made this all up right this minute; if anyone patents the idea, please send me a check.]
