I once had a stuck seat post in an old PX 10. I used CO2 to cool the post. CO2 is -109F so it should cause the post to contract slightly. One drawback, is that it creates a lot of condensation since the ambient air temp usually is that cold (unless you live in Minnesota!! ;-)) The post eventually came loose.
David Goerndt Orlando, FL (formerly from Minnesota, so I'm allowed to joke)