There are no stupid idea's in my book, only stupid responses.
But seriously, good question & suggestions;
Unfortunately, the switch-inputs (including brake, turn-signals) and the bulbs (brake, turn-signals, even headlights) are all directly connected to the ZFE.
There are no relays or other elaborate electronics in between those inputs nor outputs.
The ZFE is basically the controller who takes input (switches) and drives the output (the bulbs).
So, the only thing one could consider is to block the signal going to the bulbs, depending on the switches and, in this case, also the neutral light.
But obtaining that Neutral signal from that light won't be easy as that comes from the instrumentpanel, and that receives the neutral-signal, yep, indeed, via CAN-bus. (read: data-stream, kind of).
It won't be an easy task, and you won't be able to influence the turn-signals themselves (as these are driven by the ZFE) all but block the signal going to the turn-signals.
However, I do not know how CAN-bus will react, as it also have defective-bulb detection as well.
And I know from personal experiences that can create havoc, e.g. my factory-cruise control is adversely affected by my Kisan tailblazer.