Exactly what I was thinking. I forget if the cross bar is the same 1.66" as the cage bars. In any case one of the rubber insert sizes will fit.
Only thing is the Canadian upper seat belt mount points are a good 3-4 inches higher than the cross bar and these accessory brackets' mount holes will end up below the bar or if mounted hole up, will have the chance to rotate on the bar in a high stress event like a rollover. Mounting the bracket with the mount hole part pointing straight ahead might be the answer. That's still a good bit lower than the CF Moto 4 point harness brackets but unless the rider is tall, maybe do-able?

(The brackets are welded to an inverted U-bar on top of the cross bar. The actual cross bar is lower, about level with the top of my red gas pack here)