You can force a layout option with the filter
Shorthand version: (note that this only works with the six built-in Genesis layouts, not ones you create yourself)
For a more robust way to control your site layout, you can use this filter in conjunction with conditional tags or the template hierarchy.
Because this filter trumps everything, the custom layout options for individual Posts and Pages that you select via the Layout Settings section of your Post or Page editing screen will be ignored.
genesis_site_layout is located in lib/functions/layout.php.