functions.php

<?php
add_action( 'before_genesis_site-inner_wrap', 'do_full_width_page_header' );
/**
 * Adds a div with a background image before the site-inner wrap.
 */
function do_full_width_page_header() {

	printf( '<div class="full-width-page-header" style="background: url(\'%s\');"></div>',
	       wp_get_attachment_image_url( 2623, 'full' )
	);
}