The tubes are a pain. If you are equipped to tap threads into a hole, you can make a button out of a small screw. Then the question becomes how to attach the bar. I'd probably drill a couple small holes, tap, and then thread in tiny screws to act as pins, letting the bar ride on them. All this depends on how comfortable you are will doing the sort of thing I'm describing, and getting the tools and fasteners necessary if you don't have them.