Places the Helpful shortcode at the end. (No guarantee that it will work)

functions.php

<?php // functions.php

/**
 * Show Helpful after the content.
 *
 * @global $post
 *
 * @param string $content
 *
 * @return string
 */
function helpful_after_content_high( $content ) {
	global $post;

	if ( ! is_archive() && is_singular() && 'post' === get_post_type( $post ) ) {
		$content .= do_shortcode( '[helpful]' );
	}

	return $content;
}

/**
 * Fires the function. PHP_INT_MAX tries to load Helpful always at the end.
 */
add_filter( 'the_content', 'helpful_after_content_high', PHP_INT_MAX );