In order to make an option only visible to admin and not to end-users, set the option to 'Hidden'.

1. Click Dashboard
2. Click Attendee module
3. Click Settings button
4. Click Registration Setup in the horizontal menu
5. Select Registration Fields
6. Click the Edit button beside the field with the options
7. Click the Edit button beside the option
8. Set Display to 'No'
9. Scroll down and click Update Option to save changes.
   An admin will be the only person who will be able to select this option on a registration form