Drop this in functions.php in any Genesis HTML5-enabled theme to add a widget area after single posts.

after-entry-widget.php

<?php // Get rid of this tag

//* Register widget areas
genesis_register_sidebar( array(
	'id'          => 'after-entry',
	'name'        => __( 'After Entry', 'theme-prefix' ),
	'description' => __( 'This is the after entry section.', 'theme-prefix' ),
) );

//* Hooks after-entry widget area to single posts
add_action( 'genesis_entry_footer', 'my_after_entry_widget'  ); 
function my_after_entry_widget() {

    if ( ! is_singular( 'post' ) )
    	return;

    genesis_widget_area( 'after-entry', array(
		'before' => '<div class="after-entry widget-area"><div class="wrap">',
		'after'  => '</div></div>',
    ) );

}

after-entry.css

/* After Entry
--------------------------------------------- */

.after-entry {
    background-color: #ddd;
	border-bottom: 1px solid #222;
	border-top: 2px solid #222;
	margin-top: 40px;
	margin-top: 4rem;
	padding: 30px 0;
	padding: 3rem 0;
}

.after-entry p:last-child {
	margin-bottom: 0;
}

.after-entry .widget {
	margin-bottom: 30px;
	margin-bottom: 3rem;
}

.after-entry .widget:last-child {
	margin-bottom: 0;
}