There is a trick that I have used with bitmap sprites that may work with a swf.
Just add the swf sprite to the scriptInstanceList of the the Transparent sprite.
-- Transparent sprite behavior
on beginSprite me
SwfSpriteNum = 10
I have try it but does not work
If your transparent sprite has opaque parts then you can set the ink property to "matte" and then mouse clicks will pass through.
If your transparent sprite is a completely transparent rectangle then I suggest deleting it and using some lingo code to determine if a mouse click is inside the drag area.
the mouseDownScript = "checkMouse()"
put "checking mouse loc"
TransparentRect = rect(150,80,470,320)
if _mouse.mouseLoc.inside(TransparentRect) then
put "mouse click inside transparent Rect"
-- add drag code here