dynamic gtin

Need help with making gtin code dynamic.  This code is on our receipt page of website inside google customer reviews tag.

The data needs to come from products::upc

code on receipt page needs to add gtin for each item on the order, so if customer orders 3 items the code needs to look like this:

"products": [{"gtin":"GTIN1"}, {"gtin":"GTIN2"}, {"gtin":"GTIN3"}]

Where the "GTIN1", "GTIN2", and "GTIN3" are replaced with products::upc data and the number of gtin needs to equal quantity of different products ordered.

displaying upc might be simple like [item-upc] or something, but how do I make the gtin dynamic so it matches all items ordered?

would 
"products": [item-list][{"gtin":"[item-upc]"}][/item-list]  work?


Steve Bronson 
Air Delights, Inc.
http://www.airdelights.com
[email protected]
Phone: 1-800-440-5556
Fax: 1-503-643-8224

Air Delights, Inc. is a National Distributor of Plumbing Products and Restroom Accessories. Please visit our website at http://www.airdelights.com