Problems with including files in a cronned file with open basedir on

[occhiodesign]

I have a file in
/var/www/vhosts/domain.nl/lib/cron/cronned-test.php (the file that is cronned)
The cron, set by me in the Plesk Control Panel, runs perfectly on the file when I don't use the include() or require() command!

BUT, I want to make a php-include from /var/www/vhosts/domain.nl/config/siteconfig.php in this cronned-test.php file.

==== cronned-test.php : start ======
<?php // cronned-test.php file in /var/www/vhosts/domain.nl/lib/cron/
// include config file
include('/var/www/vhosts/domain.nl/config/siteconfig.php');

// echo variable from siteconfig
echo $web_basedir;
?>
==== cronned-test.php : end ======

If got open_basedir turned ON, but I set in vhost.conf that /var/www/vhosts/domain.nl/config should be accessable.
This work fine when I work(php) with normal files, but an error occurs when I cron the file.

The problem seems to be that a cronned file is runned as a domainuser, but the (custom) vhost.conf of this domain is ignored and, as a result I cannot include the file ("File(/var/www/vhosts/domain.nl/config/siteconfig.php) is not within the allowed path(s): (.) in /var/www/vhosts/domain.nl/lib/cron/cronned-test.php on line 3 ")

Does anyone know how I CAN include a file from another folder?

We have Plesk 8.1.0