A quick and dirty solution would be to change the StringToFile java action with something like:
StringUtils.stringToFile(getContext(), value.replace("\n","\r\n"), destination);
This would replace LF with CRLF. You could play around with replaceAll or replaceFirst depending on the desired results.
Edit: Dive into the java StringToFile action, change the code into something like this (not tested)
StringUtils.stringToFile(getContext(), value.concat(System.getProperty("line.separator")), destination);
You probebly need to change the java action of the community commons a little or ask for a feature request. Java will probebly pick your default line_feed char depending on the OS it is installed on. So if you want to export it using the CRLF you would need replace the "LINE_SEPARATOR_UNIX" char with the "LINE_SEPARATOR_WINDOWS" char. before you write it to an input stream.