boomhauer, I've considered that shims might work.
I've also wondered if I could cut and rebraze the aluminum bars with a wider 31.8 section.

I'm not sure that would be cheaper than having someone build me a custom set of aluminum bars.

Saddlesores, finding clip-on bars isn't the hard part-- mounting them while using a Jones bar is the hard part.

I'd post links and/or pictures, but I'm still too new here for that.