Still, there is another way by making a separate php page in the root, and then using iframes. That method has been described here.
Check here...
<?php
include("mainfile.php");
include(XOOPS_ROOT_PATH."/header.php");
$xoopsOption['show_rblock'] = 0;
?>
<iframe SRC='your link' name='zone1' width='100%' height='1120' marginwidth='0' marginheight='0' hspace='0' vspace='0' frameborder='0'>
</iframe>
<?
include(XOOPS_ROOT_PATH.'/footer.php');
?>