like this?
$TeamMember = new WA_MySQLi_RS("TeamMember",$DBConnection,0);
$TeamMember->setQuery("SELECT * FROM staff WHERE Live = 1 AND (StaffLocation = ? OR StaffLocation=0) ORDER BY StaffOrder ASC");
$TeamMember->bindParam("i", "".(isset($_GET['loc'])?$_GET['loc']:"") ."", "-1"); //StaffLocation
$TeamMember->execute();