rather than using wedges, I would suggest making up some C clamps with the screw portion pushing down on the rib. You can bend 1/2" square stock (using a torch) into a sort of square U shape to make the body of the clamp. The top of the U (the portion opposite the screw) should be long that it presses on both barrels.
In my limited experience, with wedges under wire bindings, the wires often slipped as I tried to tap them tighter.

cheers Doug