Wordpress Twenty Eleven theme sidebar tweak

Hi, I'm using a customized version of the Wordpress Twenty Eleven theme. You can see the installation at a staging location at [login to view URL] The default for the site is no sidebar. I need the ability to create specific single posts or pages with a sidebar. The sidebar should show just for those specific posts or pages. For some reason I'm not able to create such posts/pages. It's important that the look and feel of the existing, default full-width remains unchanged. As the main deliverable for this project, I need you to either show me how to create these posts / pages with the existing configuration, or, if that's not possible, make the necessary tweaks so that I get that option. I also need a detailed description of whatever solution you will have created for using it and for migrating it to the production site. I can give you WP admin access to the Amazon staging site above, plus ssh and sftp access (both require use of a private key which I will send you if we do this project together). I need this turned out within 24 hours, the quicker the better. I will pay $30 for this. Thank you. Marc.