Limited Items on Pay with a Like / Tweet

Hi Guys,

we're doing a big event, and as part of the event, I want people to be able to "pay with a like" to download their meal vouchers for the day.

So - here's the idea.

We have 4 restaurants that offer vouchers.
i'll make them into downloadable pics,
and load them on my website.
Generate QR's so people can pick a restaurant, and go fetch their voucher.

however -
we're a whole lot of people, and the restaurants have limits to the number of folks they can accommodate?

So I need to cap the downloads at like 50 vouchers per restaurant?

How do i go about that?

I don't have a full e-commerce solution installed on my website, and would like to skip that if possible?

Can i do that with pay-with-a-like plugin? or do i have to make another plan?