enhanced ecommerce and GTM UA

Using GTM and Enhanced eCommerce: I need to track eCommerce on a third-party system and the required ID field is not called ID or transactionID ... it is called confirmID. I'm trying to retrieve a few values from the purchase including transaction amount and cannot use the dataLayer so I'm using a custom JavaScript variable in GTM and have built a tag to read data from the custom variable.

How can I make this work if my ID field name does not match the required ID field name? Here's my JavaScript variable:

    function() {
  var ecommerceData = {
    'ecommerce': {
      'purchase': {
        'actionField': {'confirmid':'T123456',
          'tik_value':'500.00',
          'pids':'800911',
          'discounts':'chipster' }


        }
      }
  };
   return ecommerceData;
}