Inside my controller, as long as result is Traversable or is an object with public props it works...

JsonModel

    public function getTransactionDataAction()
    {
        try {
            if ($this->transaction == false || $this->transaction->getStatus() != Transaction::STATUS_COMPLETED) {
                return $this->envelopeResult(false, sprintf(self::ERR_INCORRECT_TRANSACTION, $this->_transaction));
            }

            return $this->envelopeResult(true, $this->transaction->toArray());
        } catch (\Exception $e) {
            return $this->envelopeResult(false, $e->getMessage());
        }
    }

    /**
     * Envelopes the result in an succes or error json
     *
     * @param type $success
     * @param type $result
     * @return \Zend\View\Model\JsonModel
     */
    protected function envelopeResult($success, $result)
    {
        if ($success) {
            $result = new JsonModel(new \ArrayObject(array('result' => $result)));
        } else {
            $result = new JsonModel(new \ArrayObject(array('error' => $result)));
        }

        $result->setTerminal(true);

        return $result;
    }