MainWindow.cs

 public partial class MainWindow : Window
    {
        private Session _session;
        private Project _project;

        public MainWindow()
        {
            InitializeComponent();

            Closing += MainWindow_Closing;
        }

        void MainWindow_Closing(object sender, System.ComponentModel.CancelEventArgs e)
        {
            _session.Dispose();
        }

        private void Button_Start(object sender, RoutedEventArgs e)
        {
            if (_session == null)
            {
                var sessionMgr = SessionManager.Create("MyHostApp");
                _session = sessionMgr.CreateSession();
            }
            _session.Ide.Show();
        }

        private void Button_New(object sender, RoutedEventArgs e)
        {
            if (_session == null || _project != null)
            {
                //Error handling...
                return;
            }
            var storage = ProjectStorage.CreateStorageFromTemplate("template.vstax",
                                                "csaddin",
                                                "VSTASample",
                                                null);

            _project = _session.LoadProject(storage);
        }

        private void Button_Save(object sender, RoutedEventArgs e)
        {
            if (_project != null)
            {
                MyProjectStorage outputProject = new MyProjectStorage("ProjectName");
                _project.Save(outputProject);
            }
        }

        private void Button_Run(object sender, RoutedEventArgs e)
        {
            var binaryManager = _project.BinaryManager;

            // Find the BinaryItem for the output assembly and its .pdb file.
            string assemblyName = binaryManager.AssemblyName;
            string pdbName = Path.GetFileNameWithoutExtension(assemblyName) + ".pdb";
            
            BinaryItem assemblyItem = null;
            BinaryItem pdbItem = null;

            foreach (BinaryItem item in binaryManager.GetBinaryItems())
            {
                string itemName = item.Name;
                if (String.Equals(itemName, assemblyName, StringComparison.OrdinalIgnoreCase))
                {
                    assemblyItem = item;
                    if (pdbItem != null)
                        break;
                }
                else if (String.Equals(itemName, pdbName, StringComparison.OrdinalIgnoreCase))
                {
                    pdbItem = item;
                    if (assemblyItem != null)
                        break;
                }
            }

            if (assemblyItem == null)
            {
                //Error handling...
                return;
            }

            // Get the assembly as a byte[].
            Stream assemblyStream = assemblyItem.GetStream();
            byte[] assemblyBytes = new byte[assemblyStream.Length];
            assemblyStream.Read(assemblyBytes, 0, assemblyBytes.Length);

            // Get the .pdb as a byte[].
            Stream pdbStream = pdbItem.GetStream();
            byte[] pdbBytes = new byte[pdbStream.Length];
            pdbStream.Read(pdbBytes, 0, pdbBytes.Length);

            // Load the raw assembly.
            Assembly assembly = Assembly.Load(assemblyBytes, pdbBytes);

            // Find the AddIn class.
            Type addInType = assembly.GetTypes().FirstOrDefault((t) => t.Name == "AddIn");

            if (addInType == null)
            {
                //Error handling...
                return;
            }

            // Find the Init method.
            MethodInfo initMethod = addInType.GetMethod("Init");

            if (initMethod == null)
            {
                //Error handling...
                return;
            }

            // Find my custom method.  this only works because i regenerated manifest.xml
            MethodInfo customMethod = addInType.GetMethod("Custom");

            if (customMethod == null)
            {
                //Error handling...
                return;
            }

            // Initialize the add-in
            initMethod.Invoke(null, null);
        }
    }