Balanced BNC cables?
One way (imo, it could be considered standard) exists:

1) replace your coax cable with a twinax double shielded cable

2) terminate the cable at both sides by a BNC styled twinax connector


various types exist, 3-lag, "hermafrodite", etc... select available one
connect the first cable shield to (only) one side connector, the second shield to (only) another side connector


3) use BNC twinax adapters to properly ground the shields and comfortably interface with normal BNC equipment

As stated here, "Other authors have concluded that two braided shields can help to reduce noise coupling by 20 to 30 dB."