Can I upgrade from Mountain Lion To Mavericks without the app store?
In short: No, at least not yet.

What's wrong with creating an Apple ID? Your computer won't be tied with it as you can simply signout.
Even after installing Mavericks you have to set up an Apple ID, or skip the part afterwards.

You don't have to keep it connected.

Sidenote: You create an account here, but an Apple ID is one step too far?