Display comments from one post on a different post

How do I display comments from one post on a different post?

Im trying to add another comment box onto an existing page that will show comments from a different post. How do I do this?

I tried using this code

<?php $wp_query->is_single = true; ?>
<?php comments_template(); ?>

But I dont know how to get it to display comments from a specific post? Any help?

Thanks