According to the latest version of documentation http://docs.jboss.org/hibernate/orm/4.1/manual/en-US/html_single/#persistent-classes-dynamicmodels it should be possible to switch from POJO EntityMode to MAP.
Session dynamicSession = pojoSession.getSession(EntityMode.MAP);
"Please note that the call to getSession() using an EntityMode is on the Session API, not the SessionFactory."
but the Session API doesn't have the method getSession(...), so it's impossible to switch to the map mode. The one possibility is to set hibernate.default_entity_mode to dynamic-map in the configuration. But it will change the affects to all sessions.
I'm not sure if this is a documentation problem or missing feature.