Got it:
protected function example(...){
...
$object = Doctrine::getTable('object')->findOneById(1); //for example
...
//this worked :)
$this->getRequest()->setParameter('sf_subject', $object);
$this->forward('module', 'show');
}
public function executeShow(sfWebRequest $request){
$this->object = $this->getRoute()->getObject();
...
}