IModelConversionExtension - can't get callback to fire

Hi,

How do I get the Entity Framework Designer to open Model1.foo?

I have a working EF Designer Starter Kit working, and IModelTransformExtension works fine.
I have a file called Model1.foo but "Open With" does not have does not have the designer as an entry. What do I add?

Thanks

    [Export(typeof(IModelConversionExtension))]    [PartCreationPolicy(CreationPolicy.Shared)]    [ModelFileExtension(".foo")]    public class ModelConversionExtension : IModelConversionExtension, IPartImportsSatisfiedNotification    {