I made a few pictures of my setup. It is still a bit gluey, but it does the job very well. I used a bladeholder of a size 500 helicopter with his axle in a hollow carbon tube. And I directly glued the servo to the GoPro housing, this seemed the most solid solution.
Cool - I was also thinking about the blade holder - but I only got 450's at home... I used 1 of them as yaw on my T-copter and I think it is a bit fragile - compared to my Tricopter that has a solid 8mm shaft...
I Also used a bladeholder on my tailrotor, it is an aluminum version though so no problems there. But it took about 5 tricopter versions to get it right