New Post: Host objects that implement IExpando (IDispatchEx)

It looks like it is not possible to dynamically add properties from Javascript to host objects that implement IExpando interface (COM objects implementing IDispatchEx)

ClearScript is hitting the following in HostItem IExpando.AddField:

throw new NotSupportedException("Object does not support dynamic fields");

Am I missing something? If not, would this be something that will be implemented?