entity framework 4 IObjectSet include

Question

I am using EF4 CPT4 Code first and I have setup my ObjectContext to return IObjectSet so I would be able to Mock and test my repos. However, I now noticed that I am unable to use the .Include() method for eager loading like I would be able to if I used ObjectSet.

Is there a way to make this work???

Edit: I added this extension method:

public static IQueryable<TSource> Include<TSource>(this IQueryable<TSource> source, string path)
{
    var objectQuery = source as ObjectQuery<TSource>;
    return objectQuery == null ? source : objectQuery.Include(path);
}

And it did add the Include() method, however I now get this error:

LINQ to Entities does not recognize the method 'System.Linq.IQueryable`1[PostHope.Core.DomainObjects.SiteAnnouncement] Include[SiteAnnouncement](System.Linq.IQueryable`1[PostHope.Core.DomainObjects.SiteAnnouncement], System.String)' method, and this method cannot be translated into a store expression.