The all-win situation is a great way of marketing your product. Make sure your product is good enough so you won't let the sender down. Also, make sure the gift is worth the sender's effort while you minimize the work of composing the email for the sender to send out.
Use "mailto:" HTML tag to pre-compose the email, set the b.c.c. to yourself so you also get a copy every time the email gets sent out. Then, you process one email a time to deliver the gift to the sender.
Here's an real case example I just received using this approach:
Over the next 2 weeks, we’re super excited to show you 7 traction hacks that we’ve seen drive tens of thousands of customers. The first lesson will arrive in one hour!
Until then, we have a little bonus for you. Gabriel and I pulled together a collection of interviews we did for Traction book. We’ve transcribed these interviews with people like Noah Kagan, Jimmy Wales (Wikipedia), Paul English (Kayak), Eric Ries and more.
And, if you click here to email a friend about this free course, I’ll send this bonus to you right away. Just leave “firstname.lastname@example.org” BCC’d so we know you sent it!
Gabriel and Justin