Vampiro

class YourService extends ContainerAware
{ 

  public function switchDatabase($dbName, $dbUser, $dbPass) 
  {
    $connection = $this->container->get(sprintf('doctrine.dbal.%s_connection', 'dynamic_conn'));
    $connection->close(); // for sure ;)

    $refConn = new \ReflectionObject($connection);
    $refParams = $refConn->getProperty('_params');
    $refParams->setAccessible('public'); //we have to change it for a moment

    $params = $refParams->getValue($connection);
    $params['dbname'] = $dbName;
    $params['user'] = $dbUser;
    $params['password'] = $dbPass;

    $refParams->setAccessible('private');
    $refParams->setValue($connection, $params);

    $this->container->get('doctrine')->resetEntityMamager('dynamic_manager'); // for sure (unless you like broken transactions)
  }
}