If it's not supporting anything that would put on a lot of torque, try PVC pipe. I just used some scrap Schedule 40 3/4" to do this very thing. The ID is a little smaller than the 22.2 bar, but the OD is right for 24.5. I don't know how tight your clamp is, so you might have to sand the OD a little as it will expand in diameter slightly when you get them over the bars, but the clamp I used had plenty of adjustment. I cut the PVC ring lengthwise into two pieces and, when I compressed the clamps, they were forced to conform to the slightly larger diameter bar. You could probably just cut a slot in one side if you could slide the shim over the end of the bar to get it where you want it as the 2-pieces is a little ungainly (but not that bad). Obviously, I wouldn't do this with anything that's a potential safety issue if it slips, but these seem pretty solid and are certainly fine for a switch.