Auto adjust footer widget area depending on how many widgets present?

I have a three-widget area before my content and in the footer. A week or so ago I got a response for how to make a widget area collapse (not show) if no widgets were present. That works great — no widgets present, no widget area.

It would be great if it was possible to have the size of the widgets adjust to the space if less than three were present. In other words, if three widgets take up 33% of the space each, then if two widgets were present they would each be 50% of the space. One widget would fill the whole space. How would I go about achieving this?

Thanks for any responses or pointers.
Bill