Works great, even on pages external to wordpress.

Working just fine for me.
I’m using this plugin to allow users to login/register on any page on my site, which are almost all pages external to wordpress. You just need to apply the standard calls:
global $wp, $wp_rewrite, $wp_the_query, $wp_query;
require ‘/wordpress/wp-config.php’;
define(‘WP_USE_THEMES’, false);
require(‘/wordpress/wp-blog-header.php’);

Then, add the following calls just before </head>, to make sure the plugin sets itself up:
wp_footer();
wp_print_scripts();
wp_print_styles();

If you don’t want the footer to actually show, you can use css to hide it.