Thanks, Sixty Fiver.

I screwed the wedge nut back in so it stuck up a bit and gave it a few taps with the hammer. It budged, but it only moved enough so that the wedge nut is back to being flush with the top of the quill stem even though, at this point, it's all the way unscrewed (see here: http://img.photobucket.com/albums/v6.../iphone008.jpg).

Any other ideas?