Could you get a normal wakeboard rack and cut out the middle finger? Would need to grind it smooth and tape it so it doesn't scratch but it might work, just need to find a way to make it look pretty again. Maybe call a company and see if they can leave that finger out in the machine process.
Nice Rack makes one that should fit. I've got it and they call it a Wakesurf/Kneeboard rack. I'm thinking it's more of a Kneeboard rack because it's pretty wide.
Barry. Here is one with 4 1/4" opening with a 2 1/2 tower mount. Looks killer too. My uncle does a lot of kneeboarding so I plan to get one of these for my boat.
A couple weeks ago I did what Brian is talking about... I have old school Wake Designs racks and i didnt want to have to buy a set to match so i took one of the racks and cut the middle finger out with a Dremel and grinded it smooth and then added marine and auto weatherseal... turned out a little gheto but it actually looks good on the boat with the matching wakeboard rack on the other side of the tower.