The concept is people sign a pledge to donate an amount to Wikimedia either every month, every quarter, bi-annually or annually. For example, someone pledges $5 per month to support the Foundation. They fill in details on a form and every month the Foundation sends them a polite reminder with a quick link to the donate page with the amount filled in.
That could work. I think it is important that we try and move away from discrete fundraisers and try and get donations year round, and voluntary reminders to donate could work well.