Inserting Users Full Name

I am creating a userform and would like to be able to automatically enter the name of the person using it. The way our network is set up is Username = 1st 5 letters of surname + 1st 2 letters of forename. Due to this i cannot use

Function UserNameWindows() As String
UserName = Environ("USERNAME")
End Function

as this returns the login name as opposed to the full name. I also cannot use

Function UserNameOffice() As String
UserNameOffice = Application.UserName
End Function

due to the fact that the office settings are defaulted to "Any Authorised User" unless manually updated by the user.

The users full name is displayed at the top of the start menu, but I have so far not been able to find a way to pull that into my form.