An interesting take on this would be each day having to say "nope" to the nonprofit if you wanted to skip it. Make it an opt-out donation each morning (or a chosen time).
You could defer all the "no" dollars into a pile so the user could add a bonus dollar in the same way for another day.
Edit: I think you added this to your reply already! I love the idea, though.
To solve this exact problem our model is a bit different. Our daily email features one cause and outlines two charities addressing the problem in a different way.
(Ex Cause: breast cancer Charity 1: Research Charity 2: Support for survivors. You can choose to donate to either of those or if you don't like the cause of the day you can rollover your donation to the next day.
Rollover as much as you like :) We have a few users rolling over 10 days in a row until they hit a cause that resonates with them.
I like your idea of being able to defer a dollar and then donate it to another charity you like more. That way, you're still donating a fixed $30/month, but you can distribute it more to your liking.
I think what he was more talking about was having an invisible balance. Every month you have $30, and if you choose to opt out of a payment one day, that just means you'll have $31 for the next 30 days. And now that I've actually thought about that, it doesn't make much sense - since you're only donating 1 dollar a day. Maybe you could choose to "add my credit to today's payment", or maybe they just allow you to run your account for longer after you choose to discontinue your subscription (but that is sort of a disincentive to continue subscribing for people who commonly choose to skip payments.)
You could defer all the "no" dollars into a pile so the user could add a bonus dollar in the same way for another day.
Edit: I think you added this to your reply already! I love the idea, though.