Reflector attached to saddle?
 

Does anybody know if there is such a thing as a reflector that will attach to the rear of a bike saddle? Maybe clamped to the back of the rails. When I use a bag attached to my seatpost, I have to move my seatpost reflector down, but then it's obscured by anything attached to the rear rack.

have you considered using 3m scotchlight reflective tape?
You could cover your rear triangle drops to get a similar effect.

There's some reflective material on the back of my performance seat bag.