What if you applied some serious cold to the post, then gentle (like, hair-dryer or low-setting heat gun) heat to the tube? _Might_ help make whatever above method you choose more effective.

Seems like the rotate-and-pull method has the most promise.

With the bottom bracket out, is the bb shell "open" where the bottom of the seat tube meets it? If so, you could drizzle more oil into the tube that way.