public static class BamlReader
{
    public static object Load(Stream stream)
    {
        ParserContext pc = new ParserContext();
        MethodInfo loadBamlMethod = typeof(XamlReader).GetMethod("LoadBaml",
            BindingFlags.NonPublic | BindingFlags.Static)
        return loadBamlMethod.Invoke(null, new object[] { stream, pc, null, false });
    }
}

// Usage:
StreamResourceInfo sri = System.Windows.Application.GetResourceStream(
    new Uri("/MyAssemblyName;component/MyResourceDict.xaml", UriKind.Relative));
    ResourceDictionary resources = (ResourceDictionary)BamlReader.Load(sri.Stream);