It is up to you, depending on your desired workflow. auth.bulk_register() produces a form, so the idea would be to create a controller action to display that form in the user interface. If you instead want to use auth.register_bare(), you would have to write your own custom logic to handle the inserts. You could do this by (a) creating an interface in the web application itself via a controller and view, or (b) manually running the commands in a web2py shell. Of course, if you add a controller action to the web application, you should protect it so only a logged in administrator can access it.
Example:
@auth.requires_membership('administrators')
def invite_users():
return dict(form=auth.bulk_register())
Then create an associated view with:
Anthony