functions.php

/** Register New Widget */
genesis_register_sidebar( array(
	'id'			=> 'first-post',
	'name'			=> __( 'Widget After First Post', 'wpsites' ),
	'description'	=> __( 'Displays Your Widget Content After The First Post.', 'wpsites' ),
) );

add_action( 'genesis_after_entry', 'widget_after_first_post' );
/**
 * Brad Dalton
 * example http://wpsites.net/web-design/add-content-after-any-number-of-post-excerpts-in-any-type-of-archive/
 */
function widget_after_first_post() {
	global $post_count;

	++$post_count;

	if ( ( is_front_page() ) && 1 == $post_count ) {
	    genesis_widget_area( 'first-post', array(
            'before' => '<div class="first-post widget-area">',
            'after'	 => '</div>',
		) ); 

  }

}