Unfortunately, none of the ideas suggested here help to transfer the GPS data from my smartphone to the camera via bluetooth.
So I had a really crazy idea and got myself an old android phone to use exclusively to connect to my nikon camera.
Still I am willing to do such nasty workarounds to stay with sailfish. But I don’t know how long I’ll keep doing this and then look for a new OS beyond Google etc.
So i hope that the developers will finally get the bluetooth support for android apps up and running and I can stay happy with sailfish.