I'm not sure that is possible with the way Nuke uses HTML and displays the theme.
The blocks are generated in either your theme.php or the blocks.html
Any block that is shown will use all the html in the block.html and display it no matter what.

The only thing I could think to try would be to make another center_right.html and or left_center.html.
Basically call it block_bottom.html
You would then need to incorporate it to be called from the theme.php so it will be displayed. But you want it to be displayed AFTER all the blocks have been displayed.
More confusion than help I'm sure

oh, Frankfort, Indiana here...up by Lafayette :-)

mikem