I sat this one out for a bit until something occured to me.
2 things. 1, would a shim under the disc be acceptable? I'm not sure which way it would need to go. A shim under the disc would move it outboard. A shim between the IS mount and the caliper adaptor would move the caliper inboard. Between the adaptor and the caliper would move the caliper further from center. (some floating rotors have rivet/caliper interference issues)
2: Is it possible to install a centerlock rotor backwards? I honestly don't know, I've only ever dealt with flat steel 6 bolt. But if it is *possible* then it might help to turn it around so the rotor spokes are under compression when the wheel turns in the forward direction.