Great stuff

If you want to use it on a custom post type you need to specify that it supports

$args = array(
[...]
	'supports' => array(
		'title',
		'editor',
[...]
		'page-attributes',
	),
[...]
	'hierarchical' => true,
);

$args = apply_filters( 'my_args', $args );
register_post_type( 'my_custom_post_type', $args );

Then, if you don’t need this metabox, you can remove it:

remove_meta_box( 'pageparentdiv', 'my_custom_post_type', 'side' );

but the custom post type must be configured to allow both hierarchical and page-attributes anyway.

Thanks for this plugin you make my day.