Buy a quill-type seat post.
Have someone who knows CF repair strengthen the seat tube where the wedge will end up.

A skilled welder WOULD be able to attach a replacement ear. But it would have to be done basically one tiny bead at a time, to avoid heat build up which would otherwise degrade the CF and the lug bond.
And getting a strong seam from layering up many, many tiny spot welds is really tricky.
There are also zinc based low temperature solders which will wet to aluminium.
Might be strong enough. Might not. Might let the CF/lug bond survive. Might not.