Even if there was a plugin, it would not likely work with the Original plugin.
I do something similar with Woo, but not with a plugin. It would work with the Original too.
I created a "Freebies" category and set all the products prices to $0.00 in the pricing formula. I choose products that are between $0.01 - $0.99
I have a category description, a banner and a blog article explaining that customers can choose any product they like in the Freebies category with orders over $20.