hook_views_pre_execute(&$ view)を使用して、単一の条件を希望する複数のフィールドに拡張できます。
/**
 * Recursive looks for mentioning of $fname as field of in query QueryConditionInterface::conditions()
 * 
 * @param array $cond result of QueryConditionInterface::conditions to search in
 * @param string $fname a name oof field we are looking for
 * @param array $res result array containing a references of conditions having $fname
 * @param integer $rec_lvl level of recursion
 * 
 * @return array an array containing $fname mentioned in condition $res[]['field'] == $fname
 */
function dolynskyi_help_func_find_field_condition(&$cond, $fname, &$res = array(), &$rec_lvl = 0) {
    $numeric_keys = array_filter(array_keys($cond), function($k) {return is_int($k) || (substr($k, 0, 1) !== '#');});
    $rec_lvl++;
    foreach($numeric_keys as $numkey) {
        $t = gettype($cond[$numkey]['field']);
        if($t == 'string') {
            if($cond[$numkey]['field'] == $fname) {
                $res[] = &$cond[$numkey];
            }
        } elseif($t == 'object') {
            dolynskyi_help_func_find_field_condition($cond[$numkey]['field']->conditions(), $fname, $res, $rec_lvl);
        }
    }
    $rec_lvl--;
    return $res;
}
function dolynskyi_help_func_views_pre_execute(&$view) {
    if($view->name == 'appraisals_special_global_access') { // view name we wanna extend
        $fname = 'field_data_field_ap2_employee.field_ap2_employee_target_id'; // field we look for to use as source of extending
        $search = &dolynskyi_help_func_find_field_condition($view->build_info['query']->conditions(), $fname);
        foreach($search as &$v) { // looping found field references
            $or = db_or(); 
            $or->condition($v['field'], $v['value'], $v['operator']); //repeating existing field condition
            $or->condition('field_data_field_ap2_employee.field_ap2_employee_target_id', array('711'), 'IN'); //adding any extra condition
            $v = array('value'=>null, 'operator'=>'IS NULL', 'field'=>$or); // wrapping up simple condition for $fname to multiple with $fname + our extra field via OR logic
            unset($v);
        }
    }
}