Autofac: Resolving variant types with both in and out type arguments

This question is a follow up of my previous question: Autofac: Hiding multiple contravariant implementations behind one composite.

I'm trying to find the boundries of what we can do with Autofac's covariance and contravariance support. I noticed that Autofac's ContravariantRegistrationSource only supports generic interfaces with a single generic parameter that is marked with the in keyword. This seems to limit the usefulness of this feature, and I'm wondering if Autofac has other ways in extending the support of covariance and contravariance.

I must admit that I'm not asking this because of a real application design I'm working of. I'm deliberately trying to find Autofac's limits for the sake of education.

So consider the following interface:

public interface IConverter<in TIn, out TOut>
{
    TOut Convert(TIn value);
}

And the following implementation:

public class ObjectToStringConverter : IConverter<object, string>
{
    string IConverter<object, string>.Convert(object value)
    {
        return value.ToString();
    }
}

And the following registation:

var builder = new ContainerBuilder();

builder.RegisterSource(new ContravariantRegistrationSource());

builder.RegisterType<ObjectToStringConverter>()
    .As<IConverter<object, string>>();

var container = builder.Build();

With this design and configuration, I'd expect to be able to do this:

// This call succeeds because IConverter<object, string> is
// explicitly registered.
container.Resolve<IConverter<object, string>&