I made a small more general modification to the edit_in_place update action, you can use that in any action

class myTools {
 
 
  /**
   * performs update on any single column for ajax actions
   *
   * @param     string  $peer
   * @param     integer $id
   * @param     string  $field
   * @return    object
   */
  public static function updateField($peer, $id, $field, $value) {
    if (!class_exists($peer)) {
        throw new InvalidArgumentException($peer.' does not exist');
    }
 
    $method = new ReflectionMethod($peer, 'retrieveByPk');
    $object = $method->invoke(NULL, $id);
 
    $object->setByName($field, $value, BasePeer::TYPE_FIELDNAME);
    $object->save();
    return $object;
  }