Just create the file yourself, just do
while in /etc/apt/ . Specifying the default release is for running a mixed system, usually testing/unstable or testing/unstable/experimental. It's generally a bad idea to mix stable and anything, the DD's did a lot to make stable stable, and adding anything from testing or unstable or especially experimental defeats the purpose. If you want to use a package from testin/unstable, use backports or compile it yourself.