A quick work around to do this would be to create the file
/var/www/vhosts/default/htdocs/index.php
with this content:
<?
if ( strpos($_SERVER['SERVER_NAME'],"XXXXXXXXXX") !== false ) {
header( 'Location: /index.html');
} else {
header( 'Location: /disabled.html');
}
?>
(replace XXXXXXXXX with your domain name)
then create the file /var/www/vhosts/default/htdocs/disabled.html and put anything you like.
Aris