Offering Discounts as a Referral Incentive

I am finishing work on a Jiu Jitsu flashcard app, and have run into a problem.

I want my mobile app to have a referral reward program that will give the referrer and the referree each a discount on their app subscription once the referree has created a paid subscription. However, I understand that Apple and Google stores have a barriers to this functionality.

Offering premium access or in-app purchases doesn’t make sense for this app.

Is there a work around?