You can. Use the IdUnsavedValue attribute to set a default 'unsaved id' different from zero.
[Entity]
[IdUnsavedValue(-1)] // <-- insert this line.
[Table('employee')]
[Description('')]
[Sequence('employee_id_seq')]
[Id('FId', TIdGenerator.IdentityOrSequence)]
TEmployee = class(TMoonshineObject)
(***)
HTH,