Well, it seems no one can help me on this, and I kept searching. Unfortunately my search ended with the result I didn't want, which is re-building the fusionchart object everytime the container changes its size. I definitely decided myself to do this after I found this forum topic which is very clear about this, to the point that a FusionChart team member asserts that dynamic resizing of the chart is not yet implemented.
http://www.fusioncharts.com/forum/Topic1583-37-1.aspx
This is very unfortunate, and I wonder why is this so, after working with YUI charts which are much more simple from the charting point of view, but they automatically stretch to cover all of their container area.