How to make tracking number optional with Amazon Checkout?

I don't ship via a method that gives me a tracking number, and so when I go to confirm a shipment on an Amazon Checkout order (all test orders placed by me so far--the site has not officially launched) it asks for the shipping carrier, the method or whatever, and the tracking number. If I leave the tracking number blank and click the ship button, it gives me a popup saying I need to put a tracking number. 0 returns an error, but 0000 will at least let the order go through... but I don't like it as a solution. I would rather leave it blank.

I've been in contact with Amazon's Seller Central support and they said:

*Please know that, the Tracking ID is mandatory to confirm the shipment. If this is "0", confirmation is going to fail.

You can check the related code @ <zencart>/includes/modules/payment/checkout_by_amazon.php line numbers - 241 to 244.*

if($shipping_carrier == '0' || empty($shipping_service) || empty($tracking_id)){ 
$messageStack->add_session('Please fill the required values for confirming shipment', 'warning'); 
zen_redirect(zen_href_link(FILENAME_AMAZON_ORDERS, zen_get_all_get_params(array('action')) . 'action=edit', 'NONSSL')); 
} 

I request you to please make the changes accordingly and write back to us with a confirmation, whether the issue still persist.

I tried removing the part that says "|| empty($tracking_id)" but that didn't do it. Can someone who actually UNDERSTANDS php tell me if what I want is possible? That is, for the order to go through without popping up an error demanding a tracking id? Many thanks in advance.

Ok now they are saying:

Please know that, it is not possible to disable 'tracking information' as mandatory. The tracking information must be provided by all the sellers while confirming orders, to provide positive customer experience to all customers.

Order cannot be confirmed without entering the tracking information.

Not sure why they told me what part of the code to look at if there isn't a way to make it do what I want. I guess I'll keep entering "0000" as the tracking number :/
How do the rest of you who ship without tracking numbers do it?