Wrap additional carbon around the seat post to make a lip that sits on top of the seat tube. The seat post can’t slip down into the frame but can be removed/replaced. If the saddle height needs to be adjusted, add more carbon to raise the post, to lower file the carbon away to make the lip on the post higher
I’m in the process of making an aluminium clamp to go on the post as a stop but it’s proving quite time consuming with a bench drill, hacksaw and files.
A semi permanent carbon one may be easier at this point
Wrap additional carbon around the seat post to make a lip that sits on top of the seat tube. The seat post can’t slip down into the frame but can be removed/replaced. If the saddle height needs to be adjusted, add more carbon to raise the post, to lower file the carbon away to make the lip on the post higher