The easiest way to accomplish what you are asking is to place a button on your login screen called Continue without signing in, when the user clicks on that button you sign them up! In your user table you add a boolean (True/False) field called something like Account Created. If the user actually signs up you set the Account Created to true, if the user clicks on Continue without signing in you set it to false. If the Account Created is false, you hide the settings page and logout button so the user does not know they actually have an account.The email and password are randomly generated using whatever formula you want. This way you can track everything they do, and show premium content or not.
If the Account Created is set to false, you also show a button called Create Account when the user clicks on it, it will ask for a username and password, HOWEVER the action is to UPDATE the user, not to sign up a user because the user is already signed up (without them knowing it) when they clicked Continue without Account.
Hope this helps