Extend Supporter for Free Without Using a Gateway?

I want to experiment with the idea of offering supporter upgrades for free for relatively short time periods. (Monthly? Weekly?) The idea is to encourage members to return frequently to re-up (i.e., extend) their accounts to keep all the great supporter benefits. Extra space, Analytics, keep ads of their content (Supporter Advertising plugin), etc..

I'll do what I can to keep them active and returning frequently and make offers via Admin ads and newsletters. If they stop coming, I continue to benefit from any ad revenue. They show up a year later, they are good for another month (or whatever).

Is it possible to do this without them going through a payment gateway?