I did not know carbon posts could seize into an ally frame.....quite scary that...
Do you have any antifreeze? If so I would tip the bike upside down. Remove a bottle boss bolt and then put a little bit in the hole...leave it overnight.
They certainly seize in a carbon frame. My wife's Pinarello has a jammed seatpost. We have been advised that removal will involve cutting out the said seatpost. We are still wondering whether it is worth the cost as the post height is OK.
I can't imagine that anything will penetrate down far enough to help if the post is seized. Whack the post with a hammer, ie further into the seat-tube. That might free it up.
Or, heat the seat tube up as much as you can. It should expand slightly and loosen the grip. Problem there is applying enough heat without knackering the paint. Alu shouldn't need too much heating though. It may be that an electric fan heater blasting it for a while may be enough to give you that extra movement, or at least create more of a gap to allow a lubricant to capilliary-action it's way down the tube.
On the lube front. I was told to remove the seat post monthly to prevent seizing. That's why my post came with one of those little plastic clamp gizmos that marks your seat height, allowing for easy removal and re-setting.
My LBS told me that there is no cure apart from cutting it out (difficult) but as it's at the right height for me I've left it pro tem. I now remove my other bike's seat post at regular intervals to prevent a recurrence. A lesson learnt!
I remove mine regularly and have no problem. However, I got back from a long ride (96 miler) where it had been raining heavy all day and was too lazy to take mine out, big mistake; I got it out a few days later with a bit of twisting and pulling but I won't be in a rush to make that mistake again.
I'm not convinced that penetrating oil works. You've still got to break the bond that's formed. With carbon in an ali frame you have no reaction, but a layer of aluminium oxide has built up and filled the gap tightly enough to cause the post to stick. If you're going to destroy the post, first try Sheldon Brown's recommended method of putting the post in a vice and turning the bike frame. To hold the post you could use an old saddle if need be. With the way carbon is laid I reckon this twisting force won't do the post any harm.