Rear view mirror replace

Like many others, my LS's auto dim rear view mirror has failed. Rather than pay $159 for a replacement that won't last, the dealership ordered me a replacement manual dim mirror for $29 (both mirrors mfg by Donnelly). Question is - how do you remove the mirror from the mounting base glued to the windshield? I can see no set screw, and looking at the replacement base it looks like a tapered press fit. I've tried everything short of a hammer to slide it up and off - if I try to tap it off with a block and hammer I fear trashing the windshield. Had a mirror do that on an old Town Car, a big chunk of the inner glass laminate came off with the mirror base. Any suggestions???

It's tight, but it just slides off. I can't remember the specifics, though. I'd be afraid to pound on it with anything. The shock is what scares me...a gradual force like with your hand is more kind to the glass.