render a node with comments when the $node item is not available in the path

gistfile1.php

<?php

/**
 * If you want to emulate the node/%node page in a page without the $node in the path
 * you can just call the same page callback as that url: node_page_view($node);
 */

$node = node_load($nid);
return node_page_view($node);

/*
 * But, misteriously, the comments will not appear.
 *
 * A workaround will be to render the comments separately:
 */

$node = node_load($nid);
$node_view = node_view($node);
$node_view->comments = comment_node_page_additions($node);
return $node_view;

/*
 * this solution works, but is avoiding the implementation of hook_node_view of the comment
 * module. So, it will always render the comments, even if the user doesn't have permissions.
 *
 * So, instead of forcing the render of the comments, we want to find why the comments are
 * not rendered. In the implementation of hook_node_view of the comment page, on the last lines,
 * does the next check:
 * if ($node->comment && $view_mode == 'full' && node_is_page($node) && empty($node->in_preview)) {
 * 
 * As you can see, it checks node_is_page(). This function internally uses menu_get_object(),
 * as in our page we don't have the node object, the comments will not be rendered.
 *
 * So, we can fake in what page we are:
 */

$node = node_load($nid);
$_GET['q'] = 'node/' . $nid;
$node_view = node_show($node);
return $node_view;

/*
 * With this, we will have our comments working. But we will find a different issue.
 * When a page callback returns a renderable array, Drupal calls the render function.
 * While rendering a node, at some point drupal does a drupal_set_title. Overriding the title
 * of our custom page.
 *
 * We can solve that rendering the node before and just returning the HTML in the page callback.
 * And setting our title somewhere in the middle:
 */

$node = node_load($nid);
$_GET['q'] = 'node/' . $nid;
$node_view = node_show($node);
$output = render($node_view);
drupal_set_title(t('Our custom title'));
return $output;