I think it is going to be more complicated than what Garvin described. Bulletproof sets classes for the sidebars and content area based on the template configuration (left sidebar, right sidebar, both sidebars, etc). Those classes determine the width of the sidebars and content area. Additionally, bulletproof also has the ability to place navigation in the sidebars, so a sidebar container is still required under that circumstance even if there are no other sidebar items to display.
It COULD be done by changing the logic so that the <div> classes are determined by what actually needs to be emitted, and not just by the sidebar template option.
For what it is worth, my
Kinetic template has static pages with the option to
suppress all sidebars. I believe the wrapURL plugin merely emits content in an iframe, so you could use a static page and add your own iframe code to contain the external web page.