Orderby meta_value last_name via pre_user_query in WP_User_Query

user_query.php

<?php

// prepare arguments
$args  = array(
	'meta_key' => 'last_name',
	'query_id' => 'wps_last_name',
);

// Create the WP_User_Query object
$author_query = new WP_User_Query( $args );

user_query_pre.php

<?php

add_action( 'pre_user_query', 'wps_pre_user_query' );
/*
 * Modify the WP_User_Query appropriately
 *
 * Checks for the proper query to modify and changes the default user_login for $wpdb->usermeta.meta_value
 *
 * @param WP_User_Query Object $query User Query object before query is executed
 */
function wps_pre_user_query( &$query ) {
	global $wpdb;
	if ( isset( $query->query_vars['query_id'] ) && 'wps_last_name' == $query->query_vars['query_id'] )
		$query->query_orderby = str_replace( 'user_login', "$wpdb->usermeta.meta_value", $query->query_orderby );
}