[Plugin: Greg's High Performance SEO] Using with custom post type

I’ve been creating a custom post type and I’ve got it working well. The final piece of the jigsaw is to use Greg’s High Performance SEO plug in with the custom post type as I do on standard posts. The problem is that I can’t figure out how to add the input boxes to the editor page. In my functions.php file I’ve tried:
'supports' => array('title', 'editor', 'custom-fields'),
and:
'supports' => array('title', 'editor', 'ghpseo'),
but neither of them give me what I need.

For reference, here is my complete function from functions.php:

add_action( 'init', 'create_post_type' );
function create_post_type() {
	register_post_type( 'article', array(
		'label' => ( 'Articles' ),
		'singular_label' => ( 'Article' ),
		'public' => true,
		'show_ui' => true,
		'_builtin' => false,
		'capability_type' => 'post',
		'hierarchical' => false,
		'rewrite' => false,
		'query_var' => false,
		'supports' => array('title', 'editor'),
		'rewrite' => array("slug" => "article"),
		'menu_position' => 5,
		'has_archive' => 'articles',
		'taxonomies' => array('category', 'post_tag') // this is IMPORTANT for adding the input boxes
	));
    register_taxonomy_for_object_type('category', 'article');
    register_taxonomy_for_object_type('post_tag', 'article');
}

I’m guessing I’m barking up the wrong tree altogether so any pointers would be a great help.
Thanks,
James