First I decided I need the plastic part that aligns the displays, so I put some things together again.
Then I sacrificed a gooseneck microphone protector and came up with this:
The remaining problem now is firmly attaching the gooseneck to the headphones without leaving any traces. This definitely solves the headphone sound quality problem btw. These headphones are very comfortable and have some weight, so the additional weight is not bad even without counterweights.
The gooseneck is not touching my head at all, so the two screens are now just floating in front of the eyes and the backside of the gooseneck will allow to have a 150g or so counterweight.
I was able to tightly attach the gooseneck with a screw through the unneeded gearwheel hole. So still everything would be 100% reversible besides the microphone protector.
For outside light protection I'll just buy some very dense light fabric and I'll make a big hood or something.
And yep eventually some case would be nice, but I do like that blue LED now.