Similar to Franks suggestion but instead of using a placeholder you can try using Web Properties and put similar code as below into HTML Code (body) and you shouldn't need to worry about the closing divs for placeholders.

Code:
</body>
</html>
my code after html here
<?php

or my php code here

// exit will stop rest of exported page being executed/outputted ie. xaras default </body></html>
exit; 

?>