Just edit it into your copied file and set it equal to one of your category forumid's. The point is there's no "f=10" in your url so you have to supply it in the code.
I'm not sure this will work though. Try and see.
Actually, come to think of it maybe it should go at the very top right after <?php
Try this
Code:
<?php $_REQUEST['f'] = 10;
whatever one of your categories is