Add a new per-page template

Hi; thanks for the great theme! I'm interested in having some pages in my site require a user be logged on. I inserted a call to auth_redirect() into one of the page templates, and it works fine, but I'd really like to be able to add a new template and call it something like "Full Width, Login Required", so that I can select it on a page by page basis versus changing one of your existing templates. How can I do this? Thanks, Bill