UPDATE!
So last night I'm woodworking, doing some glue-ups, and I needed a spot to lay down the glue brush and also to make a little puddle of glue for dabbing into spline joints. I hadn't tossed the ashtray in the trash yet, so I used that instead of the old Tupperware lid. It worked great! The two cigar rests molded into the glass cradle flux brushes perfectly, and the puddles of glue that drip into the ashtray are easily removed once they're dry. The glass is heavier and classier than the old Tupperware lid I was using before, so I think we have a happy ending after all. At least, until such time as I drop the damn thing and it shatters...