Like previously said, soak with penetrating oil and beat out through the bottom. Normally whenever I take out a quill style stem I loosen the bolt and give it a good wack to knock the wedge down, until one day I beat and beat on the bolt with no success. So I took an extension and put it in the bottom of the fork and with one wack the wedge came loose revealing that I had beaten the stem bolt into an "S" shape. Oops. You can also try a torch through the bottom hole as well.
Soak, beat, heat.