exclude specific entity properties during export

I just ran into a situation where I was exporting a large number of custom entities and I wanted to exclude one of the objects' properties from export so that it would be set upon import. The only way I found to do this was to overwrite EntityAPIControllerExportable in includes/entity.controller.inc and modify export to unset those properties

public function export($entity, $prefix = '') {
  $vars = get_object_vars($entity);
  unset($vars[$this->statusKey], $vars[$this->moduleKey], $vars['is_new'], $vars['my_specific_property'], $vars['my_specific_property_2']);
  if ($this->nameKey != $this->idKey) {
    unset($vars[$this->idKey]);
  }
  return entity_var_json_export($vars, $prefix);
}

It would be nice to be able to define those properties in hook_entity_info like so:

  $return = array(
    'salesforce_mapping_list' => array(
      'label' => t('Salesforce List Mapping'),
      'controller class' => 'SalesforceMappingListControllerExportable',
      'entity class' => 'SalesforceMappingList',
      'base table' => 'salesforce_mapping_list',
      'uri callback' => 'entity_class_uri',
      'fieldable' => FALSE,
      'exportable' => TRUE,
      'skip export' => array('last_sync', 'hypothetical', 'etc'),

Attached is a patch that does just that - in case you agree with me.