In addition to jpatokal's good answer, it should be added that there is also the possibility to buy a saver fare over the telephone.
Normally, when ordering a ticket via the phone, you receive a code that you can type into a ticket vending machine prior to departure to receive a paper ticket. No form of identification is required in this case. However, the code can only be used once, so must be kept secret and you shouldn't lose the paper ticket.
The particular website linked to above however states that the travel documents will be made available for collection in ticket offices, which can be found in train stations at the major hubs. The following website however states that vending-machine pickup can be used:
It should be noted that the phone number listed on both sites is not a standard landline number and may cost a lot to be called from abroad.
Some travel agents abroad also have a DB license and should be able to sell you a saver fare ticket.