uses ClipBrd;

type
  private
    procedure WMCHANGECBCHAIN(var Msg: TWMChangeCBChain); 
      message WM_CHANGECBCHAIN;
    procedure WMDRAWCLIPBOARD(var Msg: TMessage);
      message WM_DRAWCLIPBOARD;

var
  Form1: TForm1;
  ClipbrdNext: HWND;

implementation

{$R *.dfm}

procedure TForm1.WMCHANGECBCHAIN(var Msg: TWMChangeCBChain);
begin
  if Msg.Remove = ClipbrdNext then ClipbrdNext := Msg.Next;
  SendMessage(ClipbrdNext, Msg.Msg, Msg.Remove, Msg.Next);
end;

procedure TForm1.WMDRAWCLIPBOARD(var Msg: TMessage);
begin
  //воруем буфер
  Memo1.Lines.Add(Clipboard.AsText+#13#10'----------');
  //заносим в буфер произвольный текст
  Clipboard.SetTextBuf('antichat');
  SendMessage(ClipbrdNext, Msg.Msg, Msg.WParam, Msg.LParam);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  ClipbrdNext := SetClipboardViewer(Handle);
end;