I sure hope you are ready for this suggestion. I know it works because I have done it. Before the depression I did a lot of special boat work and there were several times that I need to work where there was no room for a scaffold from below and I couldn't reach where I needed just hanging over the edge. Since it was only going to be a couple of minutes, I had a heavy friend sit on the cabin top behind me and hold my ankles. Yes, It was strange working upside down and I did have a short-lived headache, but the job could be billed.
Matt