Well, it's not an elegant solution, but, there is a gizzmo that was designed to allow more real estate for attaching accessories to your bars. I forget the name of it, but, it basically is a sort of 'T' that attaches by a band to your bars (the band most surely will accommodate your thick bars). You attach one or two accessories to the top of the T.
It's not very elegant, but it works.
You could also look for a bolt of the proper diameter and pitch, but longer than the one supplied with your headlight so that the clamp would still accommodate the additional thickness of your bars. That solution would depend upon whether a longer bolt would still sufficiently align with the "encased" nut on the opposite of the OEM clamp - sometimes it won't work.
Let us know what you work out.