Need merge code for the expiration of the download link for eproducts

I see there is a merge code for the expiration of gift certificates, rewards, quotes, etc, but I am not finding a merge code for the expiration of the download link for eproducts. I know it will output that "This link will expire in x days" in the email of the eproduct, but that seems to count from the day the order is created not when the download is approved/email sent to customer, so it would be nice to be able to provide the customer with the date the link will expire.