winforms combobox update both ef6 navigation property and id

My code-first EF6 Order entity looks like following:

public partial class Order
{
    ...

    public int DispatchMethodID { get; set; }
    public virtual DispatchMethod DispatchMethod { get; set; }

    ...
}

The corresponding code in the DbContext:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    ...

    modelBuilder.Entity<DispatchMethod>()
        .HasMany(e => e.Orders)
        .WithRequired(e => e.DispatchMethod)
        .HasForeignKey(e => e.DispatchMethodID)
        .WillCascadeOnDelete(false);

    ...
}

The DispatchMethod class looks like this:

public partial class DispatchMethod
{
    public DispatchMethod()
    {
        Orders = new HashSet<Order>();
    }

    public int DispatchMethodID { get; set; }

    [Required]
    [StringLength(100)]
    public string Name { get; set; }

    public virtual ICollection<Order> Orders { get; set; }

    ...
}

Now, I want to bind both my _Order's DispatchMethod AND DispatchMethodID to the selected value of a combobox:

cmbMethod.DataBindings.Add("SelectedValue", _Order, "DispatchMethodID");

However, given code only updates the DispatchMethodID property, but does not affect DispatchMethod navigation property value. What is the best practice and how should I accomplish this?

Any help appreciated.