So I was wondering how everyone was making those moon shots and I finally figured it out: here is the result!
How it's done
Or how I did it, anyway. I took off, quit the sim, and went into replay mode. Then I chose a spot in the replay, went into the free camera mode, positioned myself so the moon was behind the plane, flew backwards 3nm away from my plane, and double tapped to zoom in.
Flight was on Solo, with an Emirates 773. No flight plan, flew out of Dubai.