Burls Ti CX Di2

^This sounds very promising. If I understand it correctly, it relies on the top of the seatpost being stong enough to take the full force of the clamping bit (as in normal use there's little pressure/force on that side/axis), but a nice bit of lateral thinking all the same!

So I understand a bit better - If using a star nut or headset expander, why would the botton of the seatpost need to be cut at an angle??

the bottom of the seatpost with the star nut acts as the wedge. the angled cut will make the seatpost expand in the seat tube when thightened.
exactly like an old fashioned quill stem.