Ask HN: I've got a question about Facebook and Twitter integration

I've got an e-book that I'm writing and I want to offer it on my website for $5 to download. Now I know there are some people that won't want to pay for the e-book so I want to give them an opportunity to download the e-book in exchange for sending out a status update on facebook or a tweet saying that they just downloaded the e-book.

My question is: is it possible to integrate facebook and/or twitter into a website and let the user download a file only after they send out a tweet or status update? I have some experience with PHP but would probably have to hire someone to do the work for me.

I feel like it should be possible to check to see if they update their status/send a tweet, I'm just not quite sure how to go about doing it.

One problem I can see with this distribution model: how would you prevent people from creating a new account to send the status update/tweet if they do not want to bug their friends about an e-book they just downloaded?