what @stof is talking about is the following https://github.com/symfony-cmf/CreateBundle/blob/master/Controller/ImageController.php#L56

and yes you can have multiple managers tied to the same or different workspaces:
http://symfony.com/doc/master/cmf/bundles/phpcr-odm.html#configuring-multiple-sessions
https://github.com/symfony-cmf/cmf-sandbox/blob/magnolia_integration/app/config/config.yml#L84