Manual Custom Connection without having to leave the application

I put a TextBlock in StaffingResourceAddressListView
  <TextBlock Text="{Binding Item.StateId}" />

everything work fine
ComboBox have problem

<ComboBox Grid.Row="4"
                                  Grid.Column="1"
                                  Width="140"
                                  Height="25"
                                  Margin="2"
                                  HorizontalAlignment="Left"
                                  DisplayMemberPath="Name"
                                  ItemsSource="{Binding ElementName=LayoutRoot,
                                                        Path=DataContext.States}"
                                  MaxDropDownHeight="200"
                                  SelectedValue="{Binding Item.StateId,
                                                          ValidatesOnDataErrors=True,
                                                          ValidatesOnExceptions=True,
                                                          Mode=TwoWay}"
                                  SelectedValuePath="Id" />
 

test by your self (Cocktail ver 19545) I'll only take 2 minutes

namespace Common {
    public interface IUserSession   {
        string Name { get; set; }
    }
}
namespace Common{
    [Export(typeof(IUserSession)), PartCreationPolicy(CreationPolicy.Shared)]
    public class UserSession : IUserSession    {
        private string _name;
        public UserSession()        {        }
        public string Name {
            get { return _name; }
            set { _name = value; }
        }
    }
}
namespace TempHire {
  public class CustomDataSourceKeyResolver : IDataSourceKeyResolver {
    public IdeaBlade.EntityModel.IDataSourceKey GetKey(string keyName, string keyExtension, bool onServer) {
      if (!onServer) { return null; }
      if (string.IsNullOrEmpty(keyExtension)) { return null; }
      if (keyName != "TempHireEntities") { return null; }
      String connectionString = "";
      if (keyExtension == "PROD")      {          connectionString = @"Data Source=|DataDirectory|TempHire_Prod.sdf";      }
      if (keyExtension == "TEST")      {          connectionString = @"Data Source=|DataDirectory|TempHire_Test.sdf";      }    
      string name = string.IsNullOrEmpty(keyExtension) ? keyName : keyName + "_" + keyExtension;
      return new ClientEdmKey(name, connectionString, false, "FromResolver");
    }
  }
}
namespace TempHire {
    public class EnvironmentResolver : IConnectionOptionsResolver    {
        private static ConnectionOptions TestEnv = ConnectionOptions.Default.WithDataSourceExtension("TEST");
        private static ConnectionOptions ProdEnv = ConnectionOptions.Default.WithDataSourceExtension("PROD");
        private IUserSession _userSession;
        [ImportingConstructor]
        public EnvironmentResolver(IUserSession userSession)  {
            _userSession = userSession;
        }
        public ConnectionOptions GetConnectionOptions(string name)   {   
            if (name == ConnectionOptions.Default.Name)  {
                    switch (_userSession.Name)  {
                        case "Test": return TestEnv.WithName(ConnectionOptions.Default.Name);
                        case "Prod": return ProdEnv.WithName(ConnectionOptions.Default.Name);

                        default: return null;
                    }
                    //return ConnectionOptions.Default.WithDataSourceExtension(_userSession.Name.ToUpper()).WithName(ConnectionOptions.Default.Name);
                }
            return null;
        }
    }
}

namespace TempHire.ViewModels.Login
{  using System.Linq;

    [Export]
    public class LoginViewModel : Screen, IResult   {
        .......
        private IUserSession _userSession;
        private string _displayMemberPath;
        private BindableCollection<object> _items;
        private object _selectedItem;

        [ImportingConstructor]
        public LoginViewModel(IAuthenticationService authenticationService, IWindowManager windowManager,
                              [Import(AllowDefault = true)] IGlobalCache globalCache, IUserSession userSession)    {
            _userSession = userSession;
            DisplayMemberPath = "WithName";
            Items = new BindableCollection<object>() { new Connections() { WithName = "Test" }, new Connections() { WithName = "Prod" } };
        }
        private class Connections   {
            public Connections() { }
            public string WithName { get; set; }
        }       
        public string DisplayMemberPath        {
            get { return _displayMemberPath; }
            set  {
                _displayMemberPath = value;
                NotifyOfPropertyChange(() => DisplayMemberPath);
            }
        }
        public object SelectedItem        {
            get { return _selectedItem; }
            set  {
                _selectedItem = value;
                NotifyOfPropertyChange(() => SelectedItem);
                _userSession.Name = ((Connections)SelectedItem).WithName;
            }
        }
        public BindableCollection<object> Items    {
            get { return _items; }
            set     {
                _items = value;
                NotifyOfPropertyChange(() => Items);
                SelectedItem = _items.FirstOrDefault();
            }
        }

           LoginView after password
            <ComboBox x:Name="Items"
                  Grid.Row="3" Grid.Column="1"
                  Height="25"
                  Margin="2,2,81,2"
                  VerticalAlignment="Center"
                  DisplayMemberPath="{Binding DisplayMemberPath}" Width="137" />

Sorry, I have not. I should have time next week.