I believe all voxels within a Qubicle file/model by definition have the same absolute size. So increasing voxel resolution automatically means increasing size. More voxels — bigger object. I believe variable voxel size within the same Qubicle file would have such an impact on the whole architecture that it wouldn't be worth it. Besides this problem is solvable via other methods in case Qubicle is only a part of you3 3D pipeline. Like all kinds of scale factors, export voxel sizes etc.
EDIT: Qubicle developer said that separate matrices may have their own scale in the future. Ok, that might be close to what you want actually.