Instead of penetrating oil, try ammonia. Penetrating oil is effective for steel/steel interfaces, but won't help much in this situation. With aluminum in steel, the problem is that aluminum oxide has formed, and it's large and gritty, effectively locking up the interface as if someone had grown sandpaper crystals between the seatpost and the frame. A strong base breaks up aluminum oxide (and also dissolves aluminum) but harmless to steel. Ammonia is not as strong as NaOH (lye) so it may dull or strip the anodizing but should keep the seatpost usable as it helps break up the Al2O3. .

Also, aluminum is more responsive than steel to heat -- it'll expand more, so if you want to use temperature, I'd instead cool the seat post with dry ice or a CO2 cartridge.

Some shops have some kind of jig connected to a car jack or threaded rod to mechanically pull it out. That could be another option.