You could always load the editor using the JFactory::getEditor() method like so:
$editor = JFactory::getEditor();
echo $editor->display("desc", "", "400", "100", "150", "10", 1, null, null, null, array('mode' => 'simple'));
If not, then have a look at line 565 of plugins/editors/tinymce/tinymce.php
where the script for the simple editor starts
Hope tis helps