Incluir:
.SetFields(Fields.Include("first_name", "last_name"));
Para excluir campos:
.SetFields(Fields.Exclude("SSN","Salary"));
Para fazer os dois:
.SetFields(Fields.Include("first_name", "last_name").Exclude("SSN","Salary"));
.SetFields(Fields.Include("first_name", "last_name"));
.SetFields(Fields.Exclude("SSN","Salary"));
.SetFields(Fields.Include("first_name", "last_name").Exclude("SSN","Salary"));