You can pass any PDO option as follows:
return new \Phalcon\Db\Adapter\Pdo\MySql(array(
"host" => $options["host"],
"username" => $options["username"],
"password" => $options["password"],
"dbname" => $options["dbname"],
"options" => array(\PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => true)
));