I can see a potential method to add threaded holes at 90 degrees to the plates. But without that it feels like radial mount calipers are more work. I like them, but I have been working hard to keep things to a "flat plate" methodology and a radial mount caliper is hard to do in that case. And adding a bracket like that means getting something machined.
Basically add a notch to the hub mount plate that another plate turn 90 degrees could be be nested into to locate it and weld it solid. The plate turned 90 degrees would have to be drilled and tapped to match the radial mount caliper and probably wouldn't be difficult to be fairly precise with. But it would require machining to get the holes located in the plate correctly, not something I would expect to get right with a drill press.