Entity Framework, Code First, Update "one to many" relationship with independent associations

It took me way too long to find a solution to the scenario described below. What should seemingly be a simple affair proved to be rather difficult. The question is:

Using Entity Framework 4.1 (Code First approach) and "Independent associations" how do I assign a different end to an existing "many to one" relationship in a "detached" scenario ( Asp.Net in my case).

The model:

I realize that using ForeignKey relationships instead of Independent Associations would have been an option, but it was my preference to not have a ForeignKey implementation in my Pocos.

A Customer has one or more Targets:

    public class Customer:Person
{
    public string Number { get; set; }
    public string NameContactPerson { get; set; }
    private ICollection<Target> _targets;

    // Independent Association
    public virtual ICollection<Target> Targets
    {
        get { return _targets ?? (_targets = new Collection<Target>()); }
        set { _targets = value; }
    }
}

A Target has one Customer:

    public class Target:EntityBase
{
    public string Name { get; set; }
    public string Description { get; set; }
    public string Note { get; set; }
    public virtual Address Address { get; set; }
    public virtual Customer Customer { get; set; }
}

Customer derives from a Person class:

    public class Person:EntityBase
{        
    public string Salutation { get; set; }
    public string Title { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set  ; }        
    public string Telephone1 { get; set; }
    public string Telephone2 { get; set; }
    public string Email { get; set; }        

    public virtual Address Address { get; set; }
}

EntityBase class provides some common properties:

    public abstract class EntityBase : INotifyPropertyChanged
{
    public EntityBase()
    {
        CreateDate = DateTime.Now;
        ChangeDate = CreateDate;
        CreateUser = HttpContext.Current.User.Identity.Name;
        ChangeUser = CreateUser;
        PropertyChanged += EntityBase_PropertyChanged;
    }

    public void EntityBase_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        if (Id != new Guid())
        {
            ChangeDate = DateTime.Now;
            ChangeUser = HttpContext.Current.User.Identity.Name;
        }
    }

    protected virtual void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null) handler(this, e);
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public Guid Id { get; set; }
    public DateTime CreateDate { get; set; }
    public DateTime? ChangeDate { get; set; }
    public string CreateUser { get; set; }
    public string ChangeUser { get; set; }
}

The Context:

    public class TgrDbContext : DbContext
{
    public DbSet<Person> Persons { get; set; }
    public DbSet<Address> Addresses { get; set; }
    public DbSet<Customer> Customers { get; set; }
    public DbSet<Target> Targets { get; set; }
    public DbSet<ReportRequest> ReportRequests { get; set; }

    // If OnModelCreating becomes to big, use "Model Configuration Classes"
    //(derived from EntityTypeConfiguration) instead
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Person>().HasOptional(e => e.Address);            
        modelBuilder.Entity<Customer>().HasMany(c => c.Targets).WithRequired(t => t.Customer);            
    }

    public static ObjectContext TgrObjectContext(TgrDbContext tgrDbContext)
    {           
        return ((IObjectContextAdapter)tgrDbContext).ObjectContext;
    }
}