This is going to require some modification to the user registration solution pack that will not be supported.
You would need to Create a new column in the database for User Level .
for all other users, set the user level to one.
Then you will need to create the Guest user account, set the user name to guest and give a simple password.
You will need to modify the login to store the user level in the a session variable and create an access rule that will only access if the user level is set to 1.
then apply that access rule to pages like the profile page that the guest user account should not be able to access.
for details on user level access, see the "User Level Authentication" tutorial on the security assist support page: