Custom fields in shopfunctions.php

[hisslink]

Hello, in the tab "Product Status" you can see the list of shoppers who bought the article. I would like to add the custom fields shoppers chose to that overview (just like in the invoice).
I think I need to change something in administrator/components/com_virtuemart/helpers/shopfunctions.php, but I don't know what. Could someone help me please?
I'm using Joomla! 3.4.8 and VirtueMart 3.0.12.