u/Barkinsons

I thought this might be useful if someone ends up in my situation, it took me a bit of digging but I got the idea here https://www.youtube.com/watch?v=wU9jbwVuSCQ

The dry ice was enough to remove the seatpost by shrinking it compared to the carbon, it was absolutely caked with corrosion. Lesson learned to always use carbon assembly paste. The bike stand was not enough to secure the seatpost, you need a bench vise and clamp it on the seat mount so it's secured for twisting.