Function to render custom panel panes.

render.php

<?php
/**
 * Render a Ctools custom content pane.
 * 
 * Mostly useful for when you need to render custom content panes 
 * outside of panels.
 * 
 * @param $id
 *  Custom content pane machine name.
 * @return
 *  Rendered custom content pane
 */
function nsla_ui_render_custom_content_pane($id) {
  ctools_include('content');
  $content = ctools_content_render('custom', $id, array('name' => $id));
  return (empty($content)) ? FALSE : theme('panels_pane', array('content' => $content, 'pane' => NULL, 'display' => NULL));
}

very helpful, thanks!