That is why I suggested in an earlier thread, that you write a short .VBS file in a TEMP folder that runs a Wscript Shell, which itself runs the cmd.exe /c and code with appropriate [ />>>\ etc] paths etc…
Run using UI.openURL(full_path_to_vbs)
That way no window flashes open…
Running external program without flashing command line - #3 by Aerilius