I tend to use a comparisation,i create and attach a dropshadow to that attribute(dropshade), because you can't count the number of shadows. That's how i use it.
+ System: CountMatching("Dropshadow") < CountMatching("dropshade")
+ System: For each "dropshade"
-> System: Create object Dropshadow on layer "1" at (0, 0)
-> Dropshadow: Attach to "dropshade"
-> Dropshadow: Send to back
But i don't use it much. I just changed the dropshadow fx-file to have an offset and customizable transparency.