With 9-speed Dura Ace, components from any of the other 9-speed Shimano groups (105, Ultegra and Tiagra) can be used interchangably. If you set up a triple shifter to work with a double crank, tell your LBS to adjust it so the two "outer" clicks select the two chainrings. That way if you accidentally try to shift into a non-existant gear, you only get a slack cable, not a damaged shifter.