Автор: http://www.swissdelphicenter.ch

{....}

uses ToolsApi, Menus;

{....}

var
  item: TMenuItem;
begin
  {get reference to delphi's mainmenu. You can handle it like a common TMainMenu}
  with (BorlandIDEServices as INTAServices).GetMainMenu do
  begin
    item := TMenuItem.Create(nil);
    item.Caption := 'A Mewn caption';
    Items.Add(item);
  end;
end;