Hi, another update. I thought I’d try the bypass module alone and, despite what the manuals say, calibration without any other load was successful and I can now control the remote lights via the second Dimmer 2.
I now have this set up in two places.
I’ve a single wall switch in our bedroom with a Dimmer 2 and Bypass controlling the ceiling light, also with a Dimmer 2 and Bypass on that light circuit.
And I’ve a double wall switch in our open plan living area, with a Dimmer 2 and Bypass, each switch controlling one of two ceiling lights, each with their own Dimmer 2 and Bypass on their circuit.
So, in total - 5 Dimmer 2s and 5 Bypass to control the 3 lights - approaching £300. Not cheap, but cheaper than having to run new wiring and then replastering but with the added benefit that I can now control these lights from wall switches, Alexa and from automations.