You should be able to mount it upside down, though you'd have to make sure the weight didn't pull the grommet through your mount point. It should work otherwise. I wouldn't mount it that way with the clamp.
I am currently using this mounted upside down supporting a 26" monitor as it gives me a greater range of motion with my unconventional desk.This also allows s me to use the entire desk top for storage with the monitor acting as a screen. I've had this configuration for several months and no problems yet.
I don't remember that as an install option. This mount will rotate my 25" to full upside down if that helps. There is also an optional extension arm to add clearance from the wall/corners if needed. Steve