Okay, this finally clicked. For some bizarre reason I thought there could still be a HW gradient/quad issue using the combined gloss value, but presumably that's just confined to texCUBE, not texCUBELod, where the LOD is being completely overridden. Derp! I'm going to conveniently blame this on the Montreal heat wave. ;)
I get the object-space idea, but when you first brought it up I thought that would be completely unmanageable (storage), and so therefore I was missing something. When you later mentioned virtual texturing, I thought that it might be more possible.