How to practically customize IE context menu?

<ad:SampleDockableContent DockableStyle="DockableToBorders"
                    x:Name="DockingManagerPropertiesHost"
                    Title="Only dock to borders">
</ad:SampleDockableContent>

public partial class SampleDockableContent : DockableContent
{
  public SampleDockableContent() {
    this.InitializeComponent();
    this.DataContext = this;
  }

  protected override bool CanExecuteCommand(ICommand command) {
    if (command == DockableContentCommands.ShowAsDocument) {
      if (this.DockableStyle == DockableStyle.DockableToBorders) {
        return false;
      }
      if (this.State == DockableContentState.Document) {
        return false;
      }
    }
    return base.CanExecuteCommand(command);
  }
}

/// <summary>
/// Defines how a dockable content can be dragged over a docking manager
/// </summary>
/// <remarks>This style can be composed with the 'or' operator.</remarks>
public enum DockableStyle : uint
{ 
    /// <summary>
    /// Content is not dockable at all
    /// </summary>
    None = 0x0000,

    /// <summary>
    /// Dockable as document
    /// </summary>
    Document    = 0x0001,

    /// <summary>
    /// Dockable to the left border of <see cref="DockingManager"/>
    /// </summary>
    LeftBorder  = 0x0002,

    /// <summary>
    /// Dockable to the right border of <see cref="DockingManager"/>
    /// </summary>
    RightBorder = 0x0004,

    /// <summary>
    /// Dockable to the top border of <see cref="DockingManager"/>
    /// </summary>
    TopBorder   = 0x0008,

    /// <summary>
    /// Dockable to the bottom border of <see cref="DockingManager"/>
    /// </summary>
    BottomBorder= 0x0010,

    /// <summary>
    /// A <see cref="DockableContent"/> with this style can be hosted in a <see cref="FloatingWindow"/>
    /// </summary>
    Floating = 0x0020,

    /// <summary>
    /// A <see cref="DockableContent"/> with this style can be the only one content in a <see cref="DockablePane"/> pane (NOT YET SUPPORTED)
    /// </summary>
    /// <remarks>This style is not compatible with <see cref="DockableStyle.Document"/> style</remarks>
    Single = 0x0040,

    /// <summary>
    /// A <see cref="DockableContet"/> with this style can be autohidden.
    /// </summary>
    AutoHide = 0x0080,

    /// <summary>
    /// Dockable only to a border of a <see cref="DockingManager"/>
    /// </summary>
    DockableToBorders = LeftBorder | RightBorder | TopBorder | BottomBorder | AutoHide,

    /// <summary>
    /// Dockable to a border of a <see cref="DockingManager"/> and into a <see cref="DocumentPane"/>
    /// </summary>
    Dockable = DockableToBorders | Document | Floating,

    /// <summary>
    /// Dockable to a border of a <see cref="DockingManager"/> and into a <see cref="DocumentPane"/> but not in autohidden mode (WinForms controls)
    /// </summary>
    DockableButNotAutoHidden = Dockable & ~AutoHide
}

- (NSMenu *)toolbarMenuInWindow:(NSWindow *)window
{
    NSView *contentView = window.contentView;
    NSView *toolbarView = contentView.superview.subviews.lastObject;
    NSMenu *toolbarMenu = toolbarView.menu;
    return toolbarMenu;
}