I can't show you a working example for symfony2 but in zf2 here: Setup Doctrine 2 filters in Zend Framework 2
Anyway this should be portable to symfony2 by finding the place in your code where you enable the filter. This is the place where you can also set / add parameters like you session_id:
$id = $this->get('session')->get('current_client_id');
$filter = $entityManager->getFilters()->enable('your_filter_class_name');
$filter->setParameter('current_client_id', $id);
Please see Doctrine docs here:
Parameters for the query should be set on the filter object by SQLFilter#setParameter(). Only parameters set via this function can be used in filters. The SQLFilter#getParameter() function takes care of the proper quoting of parameters.