I got a stem off of a bike carcas on the street once. I used a large pipe wrench, a chainlink fence, the sidewalk and a large dolomitic rock to free it. Seatposts sound really fun because of the 0 leverage situation. Easiest solution may be to just drill a hole through the post, stick a few feet rebar through it and twist it off. At least that seems like it would be the most fun way to do it.