Bodge ahead warning :

Going back to a plain seatpost offers a Potential .. as they all are reduced to 22.2mm/7/8" at the squared off top.

You can make a wedge out of the lower portion of the post sawing it off at an angle*, then cramming a Star Fangled Nut
in from the angled top you can pull it Up and the star nut will grip, as you tighten a bolt (6mm) that is Long enough
to reach the top of the post ,then you have a Flat washer under the Bolt head.

*A Power Band saw will make a clean Cut .. Hacksaws blades then to wander because the Operator is only Human..