I think another way of putting it is that WordPress never really creates ANY pages until there is a request. In fact, even after that request, the page itself isn't really created with any permanence - it is just streamed to the requesting user.
Given that architecture, as Otto said, you'd have to muck with the code for the 404 handler, or possibly with the query code to redirect how a zero post author query is handled if you wanted to change it. I'm not familiar with that part of the code, but in theory, you could perform the query, and if it is an author query and the post count is zero, you could inject a post into the array that is a single "new author" post. So, one post would be displayed for all authors who haven't posted anything.
This "injection" could be done by either directly pushing a post ID into the array (if you can do that without messing up WP) or by performing a second query that will simply always return the single "no author" post.
I think you should be able to do that with a plugin structure?? If not, upgrades would be a nightmare.
Anyway, hope these thoughts are even remotely useful. :)
Best of luck,