autosaver.js

// Must be in an external file or loaded at the end of wp_footer()
jQuery(document).ajaxSend(function(e, x, a) {
	var awesome = 1;
	a.data += '&' + jQuery.param( {is_awesome: awesome} );
});

autosaver.php

<?php
add_action('save_post', 'autosave_save_custom');

function autosave_save_custom( $post ) {
	if( wp_is_post_autosave($post) && isset( $_POST['is_awesome'] ) ) {
		$is_awesome = intval( $_POST['is_awesome'] );
		$post_id = $post->ID;
		update_metadata( $post->post_type, $post_id, 'is_awesome', $is_awesome );
	}
}
?>