[russell_w_b]

Here are two options using your existing wiring, provided the wire to your bell leads back to a master or slave socket and you can terminate all cores. The colours aren't important but the numbers of the terminals are.

Option 1 is the 'modern' plug-and-socket way using the capacitor in the master LJU and wiring all bells beyond it in parallel. I haven't shown it, but you may need an additional 3k3 resistor in series with your extension bell.

Option 2 wires both bells in series through the master LJU capacitor. This arrangement will see a power-factor improvement as the two bells in series will be better tuned (electrically) to the LJU capacitor and the ringing current will be almost in phase with the voltage. But the ring will be superior! You may need one 3k3 resistor in series with both of the bells, but try without.