OK, maybe someone else on this board has more experience with this. Unfortunately, my only experience with online ticket purchase is theoretical; I only use Länder tickets in Germany (I tend to stay in a limited geographical area). However, I know there are people out there who have done this.
I went through the steps as if I were going to purchase a ticket on a Dauer-Spezial fare, and I got to a point where it asked for two things. One was an ID, which was basically a Bahn Card number (which you don't have), an EC-Karte, Maestro (which I also don't think you have), or a credit card. Below that, they asked you for a credit card (type on pull-down menu includes MC and Visa), and there was room to put in all of my credit card information. I think you have to also put in the same credit card number for ID (but there they don't require the expiration date and verification code, the number is enough). That's how they prevent agents from buying up and reselling all the good tickets.