Suggestion for super thin shim on a 31.6 post?

[54ny77]

I have a 31.6 aluminum post that I'm maxing out on torque spec and general comfort level, but it can still move if I romp on it. Normally not a big deal if it were just me on a road bike, but the problem is it's a tandem and a stoker bar is affixed to it, so that's additional torque.

Is there anyone out there who makes a super thin (1-2mm) thin shim on a 31.6?

Otherwise I was gonna use an aluminum can and get creative, along with some carbon paste.

Thanks for any tips.