Unfortunately you are stuck with those racks on that tower unless you want to custom fab something or mount aftermarket ones really high or really far forward. I think I would try and find a rack that either fits the holes for those racks or a rack that you can just drill through that plate and mount on.
How about something like this? You could maybe drill a hole and tap it to screw the rack in. Then it would fit flush with the plate and removeable.
http://onlyinboards.com/AccessorySho...oard-Rack.aspx
Another option is to use a rack like these and then drill/tap 4 holes so that you have 4 small allen bolts securing the rack to the plate. With either of these setups you would basically ditch the clamp and mount directly to the plate on the tower.
http://onlyinboards.com/AccessorySho...-Rack-(1).aspx
I guess there is another option. See what a set of the new clamp Mastercraft racks cost, just the fingers and see if there is a way to fix those to that plate on the tower. This would look and work the best but the fingers are probably a couple hundred a piece.