Write anything as an author name on an article
Create a field that allows a user to enter text.
Implement a preprocess function that changes the values available to node templates (see the source code of template_preprocess_node() for a list of
available variables).
In the preprocess function, change $variables['submitted'] using the field you defined.


To use the already existing author widget, you would have to implement hook_form_alter() such that it removes the validation function from the form. 

Now that the validation function is removed from the form, you also need a way to validate the node. For this, you can add your own validation function. This validation function would temporarily set the author field to a valid value and then call the original validation function. 

You also need a new column to store the entered value in the database. The original column is not suitable, because it only holds integers. You also have to add an extra submit handler to the form, so that your data actually gets saved.

So yes, it is possible to use the author widget. But I advice against it. You will lose the information who really created the node. You have to manually deal with loading and saving the entry. And you are giving a well established widget a different meaning.