Sure. I have the Monolock (which is supposed to be weaker than the Monokey) mounted to an aluminum plate, and that thing is sturdy enough for what you want. You would have to make it yourself, though.
Givi does make smallish saddlebag holders, which typically mount to the same points as the top rack. The Easylock saddlebags are hybrid soft/hard, and I'm happy with them on my Dorsoduro.