Page specific visibility settings of the preface blocks

Hi All

Unfortunatelly preface region can not be controlled by the visibility settings...
Any idea how to resolve?
Found this in PHP template
function phptemplate_preprocess_page(&$vars) {
// Remove sidebars if disabled
if (!$vars['show_blocks']) {
$vars['sidebar_first'] = '';
$vars['sidebar_last'] = '';
}

Modified to this:
function phptemplate_preprocess_page(&$vars) {
// Remove sidebars if disabled
if (!$vars['show_blocks']) {
$vars['sidebar_first'] = '';
$vars['sidebar_last'] = '';
$vars['preface_first'] = '';
$vars['preface_middle'] = '';
$vars['preface_last'] = '';
}

What else do I have to change?