Autofac composite pattern

I haven't implemented this or even thought it through fully, but the best syntax I could achieve is:

builder
.RegisterComposite<IService>((c, elements) => new CompositeService(elements))
.WithElementsNamed("impl");

The elements parameter to the registration function would be of type IEnumerable<IService> and encapsulate the c.Resolve<IEnumerable<IService>>("impl").

Now how to write it...