For anyone else wondering, it's an oval aero post with a blunt trailing edge.

Some bad ideas that might spur others to come up with good ideas:

Ask Canyon to ask their seatpost supplier to make a post 3 cm or so longer. They'll say no, but might be worth a shot. Maybe they sponsor a very tall pro and have already had to make one.

Have a machinist or carbon fiber fabricator come up with a reinforcement insert that can be glued into the existing post and that extends into the seat tube (and steps up to those dimensions) to help spread the leverage over a longer section. (Or, of course, have the fabricator just build a new longer seatpost, maybe with somewhat thicker walls.)

Run a guy wire from the saddle clamp to the top tube a few inches in front of the seat tube junction. How you secure the wire to the top tube and how you adjust the tension of the wire would be solvable problems.

By the way, if you do find someone willing to build a new seatpost, here's a WeightWeenies thread started by a guy who transferred an existing saddle clamp to another carbon seatpost after amputating the second seatpost's saddle clamp.