[Phico] hacks it open with a Dremel to make room for the microphone. Cardboard soaked in wallpaper paste is then used to create a papier-mache-like shell, which is then stuffed with acoustic foam.
If you want to make one of these yourself, [DJJules] has STLs for both a normal microphone stand and another for GoPro mounts. Check out the build video after the break and the sound demos on ...