- Yes, I duct taped it.
It is possible because slaves have IR sensors. They don't need visible light for triggering. I duct taped built-in flash because I don't need or want its light.
I also turned the caps on those IR sensors so that they can only pick up the bounced IR (in other words sensors are not facing the camera). That in combination with the duct tape worked for me.
Instead of duct tape it would have been way better if I used unexposed but developed color film but I didn't have any. I could have also bought an IR sensor/trigger which ignores pre-flash for 30-40€ but they didn't have them in stock at the moment.
Someone said how colors are dull now that the winter has settled in, I disagree -- manual mode, tripod, RAW, ISO 100, 4 sec, F8 (hyperfocal trick used):
If I just had a way of eliminating those damn wires and keeping the same framing it would have been a perfect shot.