Just remove the window strut and the window will stay open at all speeds, as long as you have about 1500+ RPM. If we needed less power then we would jam something between the window and the door near the hinges (tethered to the inside of the plane of course!) to stop it dropping into view.
I would leave the mic plugged in as I needed instructions from the photographer, sideslipping as needed to remove the strut. Always keep the target in view yourself, just at the level of the lower side of the window opening and it will be in perfect view of your photographer!
