I tried purple glue stick on glass, pop-off and warp. I then tried Aquanet on glass, pop-off and warp. Tried burnished tape, no go. Tried sandpaper again, no go. Then, read some more and came across the PVA glue technique. PVA on glass, no pop, no warp, permanent. Good thing my original design called for the bottom of the part to have a 200mm piece of glass stuck to it...."not.".... Yea, I'll find the right sweet spot....

I had to take a masonry chisel hammer and chip the glass off. Lifting it actually separated the glass through the horizontal and left a thin coating of glass stuck to the bottom in a few spots. It was kind of hilarious on a certain level.