I have an idea [I haven't actually tried this myself, but]:
get some lead flashing from Bunnings, and cut a bit of the right weight. you should be able to work out what area of sheet metal will weigh how much, based on the information on the label.
Make longish rectangles; wrap them around the ends of the bar.
The cost per kg might be relatively high, but you don't want much, and you can make whatever weight you want.