The software is configured to display the sideboxes INSIDE the left or right columns. Without the side-columns, no sideboxes.

You will have to customise the template code to re-structure the layout system for sideboxes and while it's probably possible, it could be a major project.

If you are looking for a "seamless" design, where the side columns are not "obvious" (ie: defined by a border or colour scheme) then you can make edits to the css to hide or re-configure these elements so that there is no clear distiction between the centre column and its two associated side panels.

You can - through clever use of categories tabs (cats in the header) and the ez-pages header and footer menues - globally disable left and right columns and yet retain important links in the site.