So here's the problem... we don't necessarily know an order has a $0.00 total when we proceed to checkout. Reason being - there may be some tax, some shipping, some anything that is applied to the order on the checkout screen. We'll know in the order total preview that this is the case - so perhaps this functionality could only work with the preview enabled. Unfortunately, we can't just make the payment method selection go away... the form is expecting it to be there. So, we have to figure out how to trick the forms API, too.

I'm happy to take this on if someone can present a solution to these issues. Otherwise, I may have to recommend just making a normal download node. You can always use a module like TAC Lite to prevent access to the download node until the user registers so you get their contact info. I've seen businesses do this with their "white papers."