Maping details collection using interface for detail

Hello
I am playing with NH + FNH 2.0.0.697 now and can define

IDictionary<string, TestEntityDetail2> Details2 { get;  }

details for master entity where detail is concrete class.
but cannot

IDictionary<string, ITestEntityDetail2> Details2 { get;  }

where details defined as interface

Next code works fine

public interface ITestEntityDetail2
{
    bool Flag { get; set;}
}
public class TestEntityDetail2 : ITestEntityDetail2
{
    public virtual bool Flag { get; set; }
}
public interface ITestEntity : .....
{
    IDictionary<string, TestEntityDetail2> Details2 { get;  }   //!! TestEntityDetail2 there not ITestEntityDetail2
}
public class TestEntity : Entity<Guid>, ITestEntity
{
    public virtual IDictionary<string, TestEntityDetail2> Details2 { get; protected set; }
}
public class TestEntityMap : ClassMap<TestEntity>
{
    public TestEntityMap()
    {
         //......
         HasMany(x => x.Details2).Table("TABLEX").ForeignKey("FK_COL")
            .DictionaryKey("KEY_COL").Component(
                    c => c.Map(.......).Column("......")
                );
    }
}

But if change TestEntityDetail2 to ITestEntityDetail2 in ITestEntity interface - I cannot define working mapping
It seems to me that it must be some construction like
1) HasMany(x => x.Details2).Table("TABLE").ForeignKey("FK_COL")

            .DictionaryKey("KEY_COL").Component<TestEntityDetail2>(
                    c => c.Map(.......).Column("......")
                );

It doesn't compiles now or
2) HasMany(x => x.Details2).Table("TABLE").ForeignKey("FK_COL")

            .DictionaryKey("KEY_COL").DictionaryValue<TestEntityDetail2>().Component<TestEntityDetail2>(
                    c => c.Map(.......).Column("......")
                );

It compiles but doesn't help

Any ideas how to define such mapping?