I don't know of a straight-forward solution via the e-junkie standard options. However, we do something sort of similar that might work for you. We offer 2 'bonus' gifts when someone buys one of our patterns, (we sell doll clothes patterns as pdf files), you can check us out at www.libertyjanepatterns.com.
Anyway, the way we do the multiple files is simple. We place the 1 buy-able file on ejunkie as a standard digital product. That's what we sell. Then we upload our free gifts to our dropbox (google it if you're not familiar) and place them in the public folder, (which means they have a publicly accessible url, but no one will know it unless you share it with them). We place that droxbox link in the 'Thank You' script portion of the ejunkie check-out. So, when someone buys a pattern they get a thank you with the links to the bonus gifts. It works great.
It sounds like you're perfectly positioned to offer a bonus gift, which of course people eat up like candy.
Good luck with it.
Liberty Jane Clothing