Rear View Mirror

A friend of mine has a 2000 Honda Accord... yesterday was really hot, and the rear view mirror decided to fall off. Kinda funny, but...how do I seperate the mirror from that mounting plate that glues onto the windshield? I've got some rear view adhesive type 11...and think it would be easier if I was not trying to glue the whole mirror unit up, but rather just the little mounting plate. It looks like just a groove and it slides off, but it will not budge. Any help is appreciated, thanks.