Well, since a FeedBlitz autoresponder is also a FeedBlitz syndication, you can create a signup form for it. So go to the signup form creation page (go here and then click this icon ) and then add test emails addresses to the autoresponder: You're subscribing to it directly here. Check the inboxes for the confirmation emails, confirm your subscriptions and off you go! The first email should arrive immediately, then the others based on the schedule.
Once it's running to your satisfaction, you can publicize your new autoresponder to enable users to sign up for it, or you can tie it to a parent feed so it will be triggered for new subscribers as they confirm their parent subscriptions.