user column in mate

        $userColumns[] = array('call_back_fun' => array(&$this,'get_days'), 'title' => 'Remaining Days');
        $this->Editor->setConfig('userColumns',$userColumns);

and then
    function get_days($row)
    {
        $whois = "<a href=\"http://whois.domaintools.com/".$row['domain']."\" target=_blank>whois</a> ";
        $diff = strtotime($row['expiry']) - strtotime(date('Y-m-d'));
        $diff_days = floor($diff/(60*60*24));
        $html = abs($diff_days)<10000 ? '<td>'.$whois.$diff_days.'</td>' : '<td> </td>';
        return $html;
    }