Joomla/Hikashop Integration with Custom PHP program -- 2

The PHP program to allow the user to enter the letters is already written. Need to add to that program to send the image of the chosen letters and the word that the letters spells to a hikashop shopping cart. Have already set up 2 custom fields for the word and the image. Need to add/change the value of the custom field (word) and the image for the letter (letter) chosen in the shopping cart. The word that the letters spell does not go into the cart for payment but needs to be displayed on the page and in the order info that goes via email to the website owner.