Step 1: Liberal PB Blaster applied each day for several days
Step 2: Very Very VERY hot hair dryer directed at outside portion of seat tube for 10-15 minutes. You want that baby to be too hot to touch, but not hot enough to damage paint or decals in the area.
Step 3: Can of Freeze-It or similar product. This stuff is sold in aerosol cans and used by janitors to remove gum and wax from linoleum floors and it will freeze the c#ap out of anything toward which you direct the spray tube (including your fingers or face, so be careful). Got my last case on eBay. Use it to freeze the seat post.
Hot tube (expands), cold post (contracts), PB Blaster (does that PBB Magic Thing) - works every time.