Apache2.0 + safe_mode

I'm unable to get safe_mode to work. I get errors like this in my error_log (linebreaks edited for readability):

    PHP Warning:  SAFE MODE Restriction in effect.  The script whose uid
    is -1 is not allowed to access /var/www/www2.slamb.org/root/test.php
    owned by uid 500 in Unknown on line 0

    PHP Warning:  (null)("/var/www/www2.slamb.org/root/test.php") -
    Resource temporarily unavailable in Unknown on line 0

    PHP Warning:  Failed opening '/var/www/www2.slamb.org/root/test.php'
    for inclusion (include_path='.:/usr/local/lib/php') in Unknown on
    line 0

I suspect the problem is that it is unable to determine the name (and thus UID) of the script because it's being called as an Apache 2.0 filter. I've tried both these configurations with the same result:

    SetOutputFilter PHP
    SetInputFilter PHP

and

    AddType application/x-httpd-php .php

Is there some other way I can configure it? Or am I way off? Thanks, Scott Lamb