How do I delete the original Filevault admin account in 10.8?

I have a clean, fairly new MacPro. I loaded 10.8 and set up an admin account "Fred". I then encrypted the whole drive using Filevault. I then migrated a User Account "Jim" from another identical MacPro. Set Jim to be an Admin account. Deleted Fred. Enabled Jim for FV login pass through/single sign on to OSX. I have not (yet) set a master password.

User management in Sys Preferences just shows Jim. When I restart the machine, FV logins for Jim and Fred appear. If I use Jim, it logs through FV into OSX as normal. If I use Fred, it logs into FV and then presents Jim's login to OSX, also normal. But I can't find a way to delete Fred's FV account. Can anyone suggest how I can delete Fred's FV login and/or change Fred's password (given that Fred doesn't existing in Sys Pref)? Thanks