Twenty Eleven Theme Sidebar Positioning with theme options

We are looking to change the branding mainimage width to about 2/3rds of the page width, then raise the sidebar up to float left or right of the main image. We want to retain the Theme Options Default layout, enabling us to switch between a left or right layout. We have been able to do this using absolution positioning but it removes the Theme Option.
Any ideas?
See layout: http://lwdesign.co.uk/wptemplate.cfm