Thanks for letting me know about Dwolla, GrayGhost. I'm not familiar with them so it's good to know about their services.
He already has reminders set up on his calendar, Christiana, so I agree with you that he should remember but he doesn't. At this point, an automated way that withdraws from his account every month would be great. As Kestra mentioned, I've was thinking a separate account might be the way to go which is used just for this purpose. Thanks so much for your responses!