You can use the Send Free Download Link function in your Seller Admin to issue a link from our system manually, with all the same security and link-expiration features of a paid link.
For orders which are not placed using E-junkie purchase buttons, we could only process the order if payment was handled via PayPal; this would be an adaptation of our eBay integration method:
I.e., PayPal would send a notification of payment to our external-IPN URL, we match the PayPal Email receiving the payment to a seller's PayPal Email in our system, then we match the Item Name paid for to the Item Name of a product in that seller's Admin, so we would then process an order for that product (issue links, emails, etc.).
We have no way to process orders which are not placed with E-junkie buttons and not paid-for via PayPal.