Thanks K-Dog...
I had the frame inverted and the post clamped in a large vise. I exerted some twisting force using the frame's own top and down tubes as a lever without any movement on the post after several attempts. I'm leery of exerting too much force in this manner because the frame isn't meant to take a load at that point in that manner. I'd be more liberal with the upward force of a slidehammer (using your idea of clamping on an old stem as an anchor) because it's basically applying the direction of force the frame is designed to bear. The Lye is a sure fire method though, albeit heat generating and messy.