Sidebar layouts question

It seems to me that it would be very useful if one could use the ‘sidebar’ style layouts in the main content area, together with an option to select the number of columns you would want the layout to render. And, preferably, to also be able to select the category for each one so rendered columns.

If such a thing is already possible by some CSS tweaking, I would like to know how to do the above with the layout 3 from the sidebar. That is, I would personally like to get the layout 3 from the sidebar split into 3 columns in the main content area.