fixed rear door glass replacement
 

I have a 2000 Jimmy 4X4 4 door and the small fixed glass panel has been broken. It looks like the old VW type of gasket on two sides with a metal channel on the side facing the other glass (front). I have only one chance to replace it (one piece of used glass in town). Can you replace the glass without disassembling the window channel? It looks like you can pop it into the metal channel and then work the gasket around it on the other two sides. Since it's a boneyard part I can take what I need for it off the donor, but my idea is to just cut the donor gasket and slip out the pane and reverse the procedure (w/o cutting gasket). Has anyone done this repair?