Dona Rosene Interiors Professional installation company uses a very sharp glass cutting bit to drill through mirror cutting a large enough hole to install appropriate hangers to hold mirror. I have seen them do it on HGTV but I would only have professionals I trust do it.
christiejlong Thanks so much for the information! I was hoping someone would tell me to "just use a suction cup!" I really love the layered mirror look but don't think i'm willing to make that kind of committment.
ElleInOregon I can't do this in my rented apartment of course so I used a nice piece of ribbon to attach to the mirror hanging wire and hung it from a brass hanger that I installed above the mirror. The ribbon is in the color that I use for accents in the bathroom and is an attractive alternate to a permanent installation.