Bill, don't you use a glass grinder to ease the edges of your cuts? When I was working with it we often took off up to 1/8" when the cuts were off. I was thinking along the lines of just cutting something close but over sized and then just easing it down to the right size. Heck I'd do it on a belt sander,I've used one to clean up cuts on 1/4 glass and single pane as well. I'm pretty sure one could easily get it close enough to glue in place, that or less desirable would be cut the tube a bit to accommodate the thickness of the glass. A good camera shop may have gels that you could cut with scissors...
