Providers who require supervising physician credentials on their outgoing prescriptions (eFax and eRxs) can easily have this information added to their profiles.
Any user with permission to edit users can go to Admin :: Manage :: Users and click on the username of the person they want to add a supervising physician to. Scroll down to the "Other Information" section and you'll see a section asking "Does this user have a supervising physician?":
If the supervisor is another user in your system you can select the "Yes, another user in this office" option, which will then prompt you to select which other user it is.
Otherwise, if they're not another user in the system you can select the "Yes, but they don't work at this office" option and you'll be prompted to fill out details for that physician:
Fill out that form (making sure to provide valid phone and fax numbers, a two-letter state code, and a 5-digit ZIP code) and then save. The next time that user generates a prescription fax you'll see the supervisor details on that eFax form, and it you're sending an eRx (electronic prescription) the supervising physician details will be attached in the underlying message sent through SureScripts.