[AlexanderT]

Nice hack. I only had a quick glance at the code. One note: It's recommended that you sanitize the $_POST variables before using them (following vB's guidelines):

$vbulletin->input->clean_array_gpc('r', array(
'field' => TYPE_NOHTML,
'value' => TYPE_NOHTML,
'value2' => TYPE_NOHTML,
));

And then use the appropriate sanitized variables (e.g. $vbulletin->GPC['field']).