The goal is to reduce the signal ingress on an antenna cable to the
lowest possible level. What if the receive end was run through a
transformer to open the ground connection. Then, a single wire was
run parallel right next to the coax for the entire length. Then
coupled out of phase with the shield on the coax itself?
Had you thought about using a transformer at the receive end that
had a symmetrical center-tapped primary winding (antenna side), with
the center-tap connected to your ground system, and then an isolated
secondary connected to the receiver?
That would shunt the common-mode currents to ground, rather than
looking like the open circuit that the choke on the shield would.
You could also do an impedance transformation from the 100 ohms of
CAT cable to your receiver's 50 ohm input.