I can see if i add
'SOMETHING' => 'audio_file'
I can get it through the cart and out the other side to come back to me in the transaction_xml_datafeed
I can also see that I can hide it and get out the other side if i put it as an extra parameter on h:
(but in this case its not associated with the item that is in the cart, but rather the top level of the order.)
So the question is:
Is it possible to pass a hidden value that IS associated with the item in the cart?