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.)
