Custom Button and Function For Wordpress and Easy Digital Downloads

We would like to have a function added to easy digital downloads. We have their reoccurring subscription mod already, we want to make it so that if someone is subscribed for a reoccurring membership when they view an image it gives them the option to download it, and if they don't have a paid reoccurring membership then the button doesn't show. Currently they have to go through checkout for each item even when it is free, we want to allow people to still purchase things individual but also be able to purchase a reoccurring membership. If you have any questions please feel free to ask. This should be pretty easy and straight forward as most of the functions are already there all we need is the button and functions added to it. Thank you and happy bidding.