I read the discussion linked above and I am curious about the offer of a FREE add-on when paying the membership with an annual billing plan. Please let me know how I can offer the free shipping to only the people who create an account on my page automatically without a code.
This could be accomplished for a reasonable fee using the Bespoke Shipping app.
Or go crazy and Shopify Plus allows for a script editor which could do similar.
Either way you are looking at most likely using a customer tag to provide the logic.