是否可以在Doctrine Entity Manager中使用Initialiser来设置实体？

I would like to pass some path variables into a doctrine entity (using Zend2) which deals with uploaded files (using http://symfony.com/doc/current/cookbook/doctrine/file_uploads.html as a basis).

I'm able to do so via the constructor (and was intending to create a factory to do this for me)

$medium = new \Application\Entity\Medium('/path/to/filestore')

but this isn't an option when I use $medium = $entityManager->find('Application\Entity\Medium', $id);

Does anyone have any ideas how best to proceed? Is it possible to tell the entityManager which factory to use to grab entities?

Thanks!