You can set your custom attribute inside checkout page summary block using below way,

app/code/{Package}/{Module}/etc/di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">    
    <!-- Set Custom attribute in chekcout page summary block -->
    <type name="Magento\Checkout\Model\DefaultConfigProvider">
        <plugin name="default_config_provider" type="Package\Module\Model\DefaultConfigProvider"/>
    </type>
</config>

app/code/{Package}/{Module}/Model/DefaultConfigProvider.php file

<?php
namespace Package\Module\Model;

use Magento\Checkout\Model\Session as CheckoutSession;
use Magento\Quote\Api\CartItemRepositoryInterface as QuoteItemRepository;

class DefaultConfigProvider
{
    private $checkoutSession;
    private $quoteItemRepository;
    protected $scopeConfig;

    public function __construct(
        CheckoutSession $checkoutSession,
        QuoteItemRepository $quoteItemRepository,
        \Magento\Framework\App\Config\ScopeConfigInterface $scopeConfig
    ) {
        $this->_scopeConfig = $scopeConfig;
        $this->checkoutSession = $checkoutSession;
        $this->quoteItemRepository = $quoteItemRepository;
    }

    public function afterGetConfig(\Magento\Checkout\Model\DefaultConfigProvider $subject, $result)
    {        
        $quoteId = $this->checkoutSession->getQuote()->getId();
        if ($quoteId) {            
            $itemOptionCount = count($result['totalsData']['items']);
            $quoteItems = $this->quoteItemRepository->getList($quoteId);

            $isbnOptions = array();
            foreach ($quoteItems as $index => $quoteItem) {
                $quoteItemId = $quoteItem['item_id'];
                $isbnOptions[$quoteItemId] = $quoteItem['isbn'];               
            }

            for($i=0;$i<$itemOptionCount;$i++){
                $quoteParentId = $result['totalsData']['items'][$i]['item_id'];                    
                $currentOption = array();
                $currentOption = json_decode($result['totalsData']['items'][$i]['options'],true);

                $newOption = $isbnOptions[$quoteParentId];

                //for set new option inside current option tab
                if(count($newOption) > 0 && is_array($newOption)){                        
                    foreach($newOption as $key=>$value){
                        if( !is_array($value) ){
                            $currentOption[] = array('value'=>$value,'label'=>$key);
                        }
                    }
                    $result['totalsData']['items'][$i]['options'] = json_encode($currentOption);
                }                    
            }
        }
        return $result;
    }
}

Magento have option in admin

System > Configuration > Payment Methods > Zero Subtotal Checkout

You can config as per your need.

Ref link : http://docs.magento.com/m1/ce/user_guide/payment/zero-subtotal-checkout.html