I would take the North and South facades of the residential tower (extended all the way to ground level -- the associated part of the office portion) and slope them slightly inward from the base up, leaving the balance of the office block squarish -- then shoot for 300m! What an awesome building that would be -- the existing base structure could then easily deal with the extra height. Please excuse the "head-image" -- this is one building that I would like to re-imagine (can't help myself).
Good man! Next week I think I will finally have some time to get down there, just got back from BC and my sisters wedding. I was the photographer, but somehow I still have 1k photos to go through.