If I understand you correctly, it would cost the 3rd party to give away your product for free? We don't have any way of automatically charging that 3rd party, but you can at least track which of your sales came via them, so you can bill them for those orders independently of us.
The simplest approach would be to have the 3rd party simply place a regular paid order with you themselves, then they could forward to their customer the thank-you email they received with a link to their download page.
For a more automated approach requiring no personal involvement from the 3rd party in placing each order, there's a few different ways you could go about providing and tracking the free downloads:
A) If this would be a one-time giveaway, obtain a list of names/emails from the 3rd party and have us import those to a Buyer Group list for a dummy product, so you could use our Updates & Newsletters service to email free Update links to those addresses for a nominal fee:
http://www.e-junkie.com/ej/help.updates.htm
In this case, you would simply count the number of emails in the list and calculate an amount to bill the 3rd party accordingly, and you may also wish to tack on your fee cost to send out the Update itself (see link above for Update fee details).
B) Create a Discount Code good for 100% off the Item Total and provide that code to the 3rd party, who could then refer buyers to your site to place a free order by entering that code in your cart. You could even provide the 3rd party with a copy of your Add to Cart button codes to place in their own site, and in this case you could optionally embed the discount code in the buttons themselves, as explained here:
http://www.e-junkie.com/ej/tips.discounts.in-button.htm
To track these free orders, you would search your Transaction Log for orders which claimed that discount code:
http://www.e-junkie.com/ej/help.transaction-log.htm
C) Create a duplicate for each of your products, each priced at 0.00 and using the "Package files from other products" setting to issue the file you'd already uploaded to the original product. If this will be a bundle giveaway for multiple files, you could create just one zero-priced product and use "Package files..." to have it issue all of your original products' files together. Then just send that 3rd party your Add to Cart button codes (or their bare link URLs) to provide in their site or email newsletters to order the free product(s). In this case, free orders must use the buttons/links you have issued to the 3rd party, so there's less chance of a discount code getting passed around in the wild. To track these free orders, you'd just search your E-junkie Transaction Log for sales of the free product(s).
Finally, bear in mind that with methods B or C, you can only accept a limited number of Free Checkouts (orders with a 0.00 order total) per day, according to your subscription plan level:
http://www.e-junkie.com/ej/free-checkout.htm
