You could always have someone 3D print a standoff/adapter for you.
If you print the part so a nut or bolt head at the required size presses into place it works pretty well. That’s how we adapt PVC junction boxes to tripods etc. In your case you could use a nut on the bottom and a bolt out the top. Print it in two halves (top/bottom) so you can press the nut in from the top of the bottom half and the bolt in from bottom of top half. Print in ABS and acetone weld two halves together.
Ha, confused yet? Sorry. Hope you get it. ABS would work fine as long as you paint it for UV and moisture protection.