Placing material across the centre column AND inside right sidebar

I'm working on a new format for one of my sites and want to be able to carry wider items across both the centre column and the inside right sidebar. You can temporaily see the site here: http://www.gbw247.info/executivepost2/

You'll notice that the material in the centre column descends a long way down the page, whereas there's white space in the two adjacent columns. I'd like to display some of this across the page.

I haven't a clue how to go about this, though I did wonder if there was a widget or the like that enables it?

Many thanks for any pointers
Graham