Generate different order ids for different stores

we have 4 different stores in our magento website.
onepagecontroller.php code:

 /**
     * Create order action
     */
    public function saveOrderAction()
    {
        if ($this->_expireAjax()) {
            return;
        }

        $result = array();
        try {
            if ($requiredAgreements = Mage::helper('checkout')->getRequiredAgreementIds()) {
                $postedAgreements = array_keys($this->getRequest()->getPost('agreement', array()));
                if ($diff = array_diff($requiredAgreements, $postedAgreements)) {
                    $result['success'] = false;
                    $result['error'] = true;
                    $result['error_messages'] = $this->__('Please agree to all the terms and conditions before placing the order.');
                    $this->getResponse()->setBody(Mage::helper('core')->jsonEncode($result));
                    return;
                }
            }
            if ($data = $this->getRequest()->getPost('payment', false)) {
                $this->getOnepage()->getQuote()->getPayment()->importData($data);
            }
            $this->getOnepage()->saveOrder();

            $redirectUrl = $this->getOnepage()->getCheckout()->getRedirectUrl();
            $result['success'] = true;
            $result['error']   = false;
        } catch (Mage_Payment_Model_Info_Exception $e) {
            $message = $e->getMessage();
            if( !empty($message) ) {
                $result['error_messages'] = $message;
            }
            $result['goto_section'] = 'payment';
            $result['update_section'] = array(
                'name' => 'payment-method',
                'html' => $this->_getPaymentMethodsHtml()
            );
        } catch (Mage_Core_Exception $e) {
            Mage::logException($e);
            Mage::helper('checkout')->sendPaymentFailedEmail($this->getOnepage()->getQuote(), $e->getMessage());
            $result['success'] = false;
            $result['error'] = true;
            $result['error_messages'] = $e->getMessage();

            if ($gotoSection = $this->getOnepage()->getCheckout()->getGotoSection()) {
                $result['goto_section'] = $gotoSection;
                $this->getOnepage()->getCheckout()->setGotoSection(null);
            }

            if ($updateSection = $this->getOnepage()->getCheckout()->getUpdateSection()) {
                if (isset($this->_sectionUpdateFunctions[$updateSection])) {
                    $updateSectionFunction = $this->_sectionUpdateFunctions[$updateSection];
                    $result['update_section'] = array(
                        'name' => $updateSection,
                        'html' => $this->$updateSectionFunction()
                    );
                }
                $this->getOnepage()->getCheckout()->setUpdateSection(null);
            }
        } catch (Exception $e) {
            Mage::logException($e);
            Mage::helper('checkout')->sendPaymentFailedEmail($this->getOnepage()->getQuote(), $e->getMessage());
            $result['success']  = false;
            $result['error']    = true;
            $result['error_messages'] = $this->__('There was an error processing your order. Please contact us or try again later.');
        }
        $this->getOnepage()->getQuote()->save();
        /**
         * when there is redirect to third party, we don't want to save order yet.
         * we will save the order in return action.
         */
        if (isset($redirectUrl)) {
            $result['redirect'] = $redirectUrl;
        }

        $this->getResponse()->setBody(Mage::helper('core')->jsonEncode($result));
    }

    /**
     * Filtering posted data. Converting localized data if needed
     *
     * @param array
     * @return array
     */
    protected function _filterPostData($data)
    {
        $data = $this->_filterDates($data, array('dob'));
        return $data;
    }

Current process happening in my site:
Customer Purchases two individual products from two different stores.
Ex: Customer purchases Product1 in Store1 & Product2 in Store2.
Order Id is being same for two stores. Store ID & Store name is being the same from where he checkouts of all the products.
i want to generate different order id’s for different stores.