Accepting Stripe coupons through Portal

I appears there are a number of threads on this topic that relate to code-based solutions (or side-stepping the Ghost implementation entirely).

To make this feature more accessible, I’d like to for there to be a toggle switch in the Portal settings so that I can turn a field on in the signup process where my subscribers can add a coupon code. I was thinking something like this:

This would enable a field in the subscription form where subscribers could add coupon codes that I’ve pre-configured in Stripe and shared. This would provide the flexibility to make offers such as ‘first x months free’, ‘50% off for life’, ‘free for life’, etc.