Adding multiple inherited instances of diferent children types in a TPT Mapping EF4.1
public abstract class Person
{
    public int Id {get;set;}
}

public class Customer : Person
{
    public string Name {get;set;}
}
public class User : Person
{
    public string Password {get;set;}
}

context.Set<Customer>().Add(new Customer { Name = "X" });
context.SaveChanges();

Persons
Id: 1

Customers
Id: 1
Name: X

context.Set<Customer>().Add(new User { Id = 1, Password = "0" });
context.SaveChanges();