I remember reading illuminati talking about how he uses a wet paper towel to dissolve the glue a bit and then lets it all dry up. I don't know if this would help your specific adherence problem; what I'm imagining is that by actively dissolving the glue to the glass you get better adhesion of the glue to the glass, this substrate layer also provides good adherence to the extruded plastic effectively coupling the two. Anyway just a thought, illuminati will likely shed more light on the subject.