procedure TForm1.Button1Click(Sender: TObject);
var
  si: TStartupInfo;
  pi: TProcessInformation;
begin
  si := Default(TStartupInfo);
  si.cb := SizeOf(TStartupInfo);
  pi := Default(TProcessInformation);
  if not CreateProcess(nil, PChar('Process.exe ' + NativeUInt(Handle).ToString()), nil, nil, True, 0, nil, nil, si, pi) then
    RaiseLastOSError();
end;

procedure TForm1.CreateWindowHandle(const Params: TCreateParams);
var
  NewParams: TCreateParams;
begin
  NewParams := Params;
  if ParamStr(1) <> '' then
  begin
    NewParams.WndParent := ParamStr(1).ToInt64();
    NewParams.ExStyle := NewParams.ExStyle and not WS_EX_APPWINDOW;
  end;
  inherited CreateWindowHandle(NewParams);
end;

NewParams.ExStyle := NewParams.ExStyle and not WS_EX_APPWINDOW;