Post up the specs on the stock rotors, offset, internal diameter of the hub area, rotor thickness and new diameter rotor you want to run and I will look for the easiest bolt on solution and let you know if there is a solution available of what it might take to make one.
On my rear DIY 4 piston BBK setup I had to have the rotor hats machined to the right offset, it was not that expensive and a one time cost which could happen in this situation.
THIS is not undercutting what DiJL1 is doing, just wanting to help those wanting a bit less weight find a way to do it, you will still need the parts he is working on and I would not profit from it except in knowing I helped a few members out