There likely isnt much you can do. I have looked into gutting them with as little destruction as possible, and have concluded that it will be difficult to say the least!!
Looking from behind, they seem to blend right into the outlet with a slight ledge that appears to only be tacked in place. A view from the front shows roughly the same thing. As I recall, the louvers in the inner pipe open to the front and inward. If a person was to carefully cut the tacks in the front and rear, the tube may slide out, hopefully dragging the glass mat with. When I get a set of replacements, I will perform surgery and post pics. Unfortunately, money is tight and it will not be all together soon. There are always more important things (roof, fence, braces, dr's, etc) to spend funds on.
Best of luck!!