Markos' idea about an 'air hammer' combined with my rube goldburg contraption (pictured) with a couple days of PB Blaster worked for me.For the headrest, I would try holding a piece of flat stock to the chrome posts. Hit the other side of the flat stock with an air chisel. That gives you hundreds of hammer hits in a minute versus a handful. The vibrations could free the post from the retainer.
Scott,Dan, i would think that you might have needed to do a pair of straps on both sides ... tighten up one, then tighten up the other side ... going back and forth.