You could compare the oldx and oldy with the currentx and currenty every tick..
so give the dragged sprite three instance variables OldX, OldY, Dragangle
DraggedSprite is dragging
--system compare two values: Draggedsprite.OldX is not Draggedsprite.X
or
--system compare two values: Draggedsprite.OldY is not DraggedSprite.Y
Draggedsprite set Dragangle = angle(Draggedsprite.x,Draggedsprite.y,Draggedsprite.oldX,Draggedsprite.oldy)
Draggedsprite set oldx = Draggedsprite.x
Draggedsprite set oldy = Draggedsprite.Y
Particle set angle = Draggedsprite.DragAngle