This same mirror issue bothered me so much in the cinematography of "Suits" that I had to email Dan Stollof the Director of Photographer. And he told me the glasses were gimbled so that the reflections of the camera and crew were angled and will not be visible on the glass.
I don't know if the same technique will work for mirrors though. Just thought to share.
Wow! That's a great short. Straight to the point with beautiful pictures.