i have the same dilema.. i solved it like this...
in each of you .php files put this at the top..
<?
$path_to_root = "../../";
$absolute_path = realpath($path_to_root);
?>
where $path_to_root is the relative path to your root directory. It's a bit messy, but it's the only way i can do it without $DOCUMENT_ROOT. oh, and btw, u can get either of those vars anywhere in your scripts with $GLOBALS['absolute_path'] or $GLOBALS['path_to_root']
etc.
hope this helps;
Ben