It's basically the same as http://www.vbulletin.org/forum/showthread.php?t=63520&highlight=css+path :)

Open adminfunctions_template.php.

Find:

$cssfilename = 'clientscript/vbulletin_css/style-' . substr(md5(microtime()), 8, 8) . '-' . str_pad($styleid, 5, '0', STR_PAD_LEFT) . '.css';

if ($vbulletin->options['storecssasfile'] AND write_css_file($cssfilename, $css))
{
$QUERY[] = "css = '" . $vbulletin->db->escape_string("<link rel=\"stylesheet\" type=\"text/css\" href=\"$cssfilename\" id=\"vbulletin_css\" />") . "'";
}


and replace it with:

$cssfilename = 'clientscript/vbulletin_css/style-' . substr(md5(microtime()), 8, 8) . '-' . str_pad($styleid, 5, '0', STR_PAD_LEFT) . '.css';
$cssfilepath = $vbulletin->options['bburl'].'/'.$cssfilename;

if ($vbulletin->options['storecssasfile'] AND write_css_file($cssfilename, $css))
{
$QUERY[] = "css = '" . $vbulletin->db->escape_string("<link rel=\"stylesheet\" type=\"text/css\" href=\"$cssfilepath\" id=\"vbulletin_css\" />") . "'";
}


Now, and that's the most important step, you have to rebuild your styles!

Have fun and click install (http://www.vbulletin.org/forum/vborg_miscactions.php?do=installhack&threadid=97273) ;)