Pretend you want it to stay right where it is and it will then fall right off! :buck:
Seriously though, I know of no way to remove one that is on as well as it should be without damaging the glass. I tried to shear off the ball on a cracked WS in my parts car and pieces of the glass came with it (as well as cracking the glass further). Maybe someone else will have some tech for you.
I had to get my rearview mount off when I swapped to a different mirror. I used an old hair dryer I keep in the shop to heat up and carefully soften the glue while gently chiseling the glue with a razorblade scraper.
I used laquer thinner to remove the rest of the glue once it was off.
Disclaimer: There is no guarantee that this method will work for you. I'm only reporting that it worked for me.
ok so its off! what worked, i soaked in laquer thinner and tryed to get it off , to no avial. but i am sure it did loosen it up, i didnt have any acetone. so after that failed, i grabed my butane torch and just went around the outside of it on the outside of the glass, and with a razor it poped right off! (my heat gun was mia) but thank you! reataching will be much easier!