What Neuroglancer displays, including the datasources, and any other options, is controlled by its JSON "state".
For example, you can see the current state by clicking on the "{}" icon at the top right of the Neuroglancer window.
The state is encoded in the URL itself, so if you want users to receive a certain view by default, you can simply provide a link or redirect that encodes that view.
In addition to using Neuroglancer interactively to create the desired view, you can also use the Neuroglancer Python API to construct such a link. (Of course you can also manually construct the JSON.)
There currently isn't any build-time option to specify a default initial state --- that could be added easily enough, but just providing a separate link/redirect to the desired initial state may serve your purposes just as well.