Add a new group to the exposed filter groups.
public function addGroupForm($form, &$form_state) {
$item =& $this->options;
// Add a new row.
$item['group_info']['group_items'][] = array();
$form_state['view']
->get('executable')
->setItem($form_state['display_id'], $form_state['type'], $form_state['id'], $item);
$form_state['view']
->cacheSet();
$form_state['rerender'] = TRUE;
$form_state['rebuild'] = TRUE;
$form_state['force_build_group_options'] = TRUE;
}