Best way to remove 72 Dart rear glass?

I have the whole car apart and ready for paint except this mother f'n rear window, I cracked the front glass trying to get the seal out in one piece!!! AAARRGH!!! oh well good buddy can get me one for $90.00, So the rear glass is loose I can lift the rubber up around the glass but it still in the channel and I don't want to break this piece!!! Any hints or tricks?? (I don't wanna cut the gasket!!!)