Umm... am I missing something obvious? I can add x_line_item hidden fields to the submission and the ordered items appear in the email which is sent to the customer.

There is no mention of what has been ordered in the email sent to the merchant though? How is the merchant to know what was ordered?!

I can create a custom email, but that sort of defeats the purpose - is there no way of adding order details to the merchant email? and if not, why on earth not?