I had highway pegs mounted on the curved part of the crash bars for years. I will assume you are talking about Kury Magnum clamps. That is what I used. That curved part is a little more than an inch. So you don't crush the tubing or garf up the chrome, you need to get 1-1/4" Magnum clamps. Get some rawhide with a thickness of approx. 1/8". Cut a strip as wide as the clamp and just long enough to cover the circumference of the bar without overlapping the ends. You may need to use a large channel lock pliers to get the ends of the clamp close enough for the bolt to reach to the opposite hole. You could also use the rubber from an old inner tube and wrap enough around the bar to get enough thickness to clamp against. Since you are mounting lights, the rubber might be sufficient...and reduce some vibration from reaching the lights.
Vibration.........

it just hit me, you must be talking about vibtation from the road!