You could try using a hair dryer to heat up the tab, or maybe a heavy
soldering iron held directly against the metal piece.  Personally I've
never been able to get one to stick for more than a couple months once
the factory glue has given up, so unless you're better at this than I
am it shouldn't be too hard :)

nate

It will never come off.
Get another one.
Glue it to the first one.
Rightside up.

I've never had this exact problem, but I have removed much epoxy. I
would try a razor blade in one of those metal blade holders. Slide it
along the window and hit a corner of the attachment. One little break
in the atachment and it should all pop off.

PS. I have good luck attaching mirror plates with JB-Weld four minute
type. I hold it in position until it sets and let it cure overnight.
The excess can easily be cleaned when it sets, but before it cures.