I bought a stock GS pole and mount from Bill @ Allison and fabricated a mount to the transom on a XR 2002 it went up thru the gas fill/pretty neat,I believe my old SS had a cutout/but not cut out if you know what I mean just behind the center of the back seat.When I spoke to Allison about the "cut out" I believe that a ski pole was a possibility but never made it to the drawing board.Keep in mind that what makes an Allison fast also makes it a not so hot slalom hull/great barefoot but not for agressive slolom skiers,I can easily pull the hull off the pad on a cut and this will be pretty scary for the driver.For ski racing you will be so far behind the boat it probably will not be a concern.
Good luck. Rolf