Fluent NHibernate HasManyToMany() IDictionary<> Composite ID problem

Question

I'm using Fluent NHibernate 1.1.1.694 which uses a slightly different syntax than FNH1.0, especially when it comes to dictionary mapping.

In my model, I have Employees, Addresses and AddressTypes (postal, physical, etc).

public class Employee
{
    // <snip other properties />
    public virtual IDictionary Addresses { get; set; }

    public Employee()
    {
        this.Addresses = new Dictionary();
    }
}

public enum AddressType
{
    Physical,
    Postal
}

public class Address
{
    public virtual int Id { get; private set; }
    public virtual IList Lines { get; set; }
    public virtual string City { get; set; }
    public virtual string Zip { get; set; }
}

My mappings:

public class EmployeeMap : ClassMap
{
    public EmployeeMap()
    {
        CompositeId()
            .KeyProperty(e => e.IdentityType)
            .KeyProperty(e => e.IdentityValue);

        // <snip other properties />

        HasManyToMany(e => e.Addresses)                
            .Inverse();
    }
}

The following .hbm.xml snippet is generated:

<map inverse="true" name="Addresses" table="EmployeeAddresses" mutable="true">
    <key>
        <column name="Employee_id" />
    </key>
    <index type="Domain.Entities.AddressType, Domain, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null">
        <column name="Key" />
    </index>
    <many-to-many class="Domain.Entities.Address, Domain, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null">
        <column name="Address_id" />
    </many-to-many>
</map>

The .hbm.xml that I'd like to generate is

<map inverse="true" name="Addresses" table="EmployeeAddresses" mutable="true">
    <key>
        <column name="IdentityType" />
        <column name="IdentityValue" />
    </key>
    <index type="Domain.Entities.AddressType, Domain, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null">
        <column name="Key" />
    </index>
    <many-to-many class="Domain.Entities.Address, Domain, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null">
        <column name="Address_id" />
    </many-to-many>
</map>

Obviously this will fail, because nowhere am I telling it that there is a composite ID to use for the parent key. But I can't find the methods to tell it. The .Columns and .ParentKeyColumns don't exist for .HasManyToMany<Key,Value>()

How should I map this?