I framed it out with some MDF. I had to cut some notches to make room for the clips on the top (sorry, no pictures of that), and then I glued the frame onto the mirror with gorilla glue. Is that how it's done? I don't know, but that's how I did it. The mirror and the frame are now one.
I painted it black so that it would match the newly painted cabinet below. However, I forgot the little detail about the backside of the frame reflecting in the mirror. Oops.
No worries. I have lots of cove molding hanging around from the door trim. So I painted up a few front AND back and trimmed out the frame.
Ahhhh. Better. I still need to do a little touch up paint, but I'm calling this mirror done.