idk if they do that but you could just cancel your subscription after the first payment goes through
I'm horribly wary of all kinda subscriptions :I
Yes RfK nailed it.. you set it up, either do your one time value and cancel after the first billing, (which you are notified) or just plan a split-up and set it lower and let it roll.
Either way, I view it as money both well spent (for my entertainment dollar) and money well earned for TPL