I've looked into those, but they are not something I'd want to use for every ride. Also, I don't use the multiple mount point racks, only the beam racks. Much easier to detach & stow it separate from the bicycle, that's mounted outside on a vehicle.

I think, if one is designed for a beam rack as described, it'd be the first for supporting those of us with beam racks & open up more traveling opportunities for the weight weenies too.