StructureMap HowTo: Conditional Construction on Deep Object

Question

I'm having difficulty conditionally creating a dependency. Googling, I have yet to find a good example of using the BuildStack and Conditional Predicates.

Here's what I'm doing in the Registry:

//snip

public SomeRegistry()
{
    this.InstanceOf<IFoo>().Is.Conditional(
        c =>
            {
                c.TheDefault.Is.ConstructedBy(() => new FooZ());

                c.If(
                    p => p.ParentType.IsAssignableFrom(typeof(IBar)) &&
                            p.BuildStack.Current.RequestedType.IsAssignableFrom(typeof(IDoStuffWithFooA)))
                            .ThenIt.Is.ConstructedBy(() => new FooA());
                c.If(
                    p => p.ParentType.IsAssignableFrom(typeof(IBar)) &&
                            p.BuildStack.Current.RequestedType.IsAssignableFrom(typeof(IDoStuffWithFooB)))
                            .ThenIt.Is.ConstructedBy(() => new FooB());
            });

    this.Scan(
        s =>
            {
                s.TheCallingAssembly();
                s.WithDefaultConventions();
            });
}

//snip

Here's unit tests showing what I'm expecting

//snip

[TestFixture]
public class ConditionalCreationTest
{
    [Test]
    public void GiveUsFooAWhenDoingStuffWithA()
    {
        var dependA = ObjectFactory.GetInstance<IDoStuffWithFooA>();

        Assert.IsInstanceOfType<FooA>(dependA.Foo);
    }

    [Test]
    public void GiveUsFooBWhenDoingStuffWithB()
    {
        var dependB = ObjectFactory.GetInstance<IDoStuffWithFooB>();

        Assert.IsInstanceOfType<FooB>(dependB.Foo);
    }

    [Test]
    public void GiveUsFooZByDefault()
    {
        var foo = ObjectFactory.GetInstance<IFoo>();

        Assert.IsInstanceOfType<FooZ>(foo);
    }

    [Test]
    public void GiveUsProperFoosWhenWeDontAskDirectly()
    {
        var bar = ObjectFactory.GetInstance<IBar>();

        Assert.IsInstanceOfType<FooA>(bar.DoStuffA.Foo);
        Assert.IsInstanceOfType<FooB>(bar.DoStuffB.Foo);
    }

    [SetUp]
    public void SetUp()
    {
        ObjectFactory.Initialize(a => a.AddRegistry<SomeRegistry>());
    }
}
//snip

This is what I want StructureMap to AutoWire with the correct dependency of IFoo:

//snip
    public class Bar : IBar
    {
        private IDoStuffWithFooA doStuffA;
        private IDoStuffWithFooB doStuffB;

        public Bar(IDoStuffWithFooA doStuffA, IDoStuffWithFooB doStuffB)
        {
            this.doStuffA = doStuffA;
            this.doStuffB = doStuffB;
        }

        public IDoStuffWithFooA DoStuffA
        {
            get
            {
                return this.doStuffA;
            }
        }

        public IDoStuffWithFooB DoStuffB
        {
            get
            {
                return this.doStuffB;
            }
        }
    }
//snip

I cannot figure out how to get GiveUsProperFoosWhenWeDontAskDirectly test to pass.

I want to get FooA to get initialized when I need IDoStuffWithFooA, FooB when IDoStuffWithFooB, regardless of when it's needed in the graph. What is the proper syntax for the conditional predicate?