Integrate Pay With a Like Into Marketpress

I currently have a few eBooks I'm selling on my site at using MarketPress however I wanted to ask whether it is possible to alter the payment system so that I can maintain the ordered layout and product descriptions but instead of collecting a cash payment for a download, the user simply "pay" with the social share.

I tried enabled Pay with a Like in Marketpress but for some reason I can't get it to hide the content behind a paywall.

Also - I tried creating a custom post type for my materals but the problem with that is I don't want to recreate the MarketPress interface - plus I would like to use the MP download system so people can't copy paste the eBook URL and send it out.

Thanks very much in advance!