Well, if you copy that disc completely, you will get all content from the source. By switching off the subtitles while viewing only the so called forced subtitles should be shown. If you ripped only the main movie or any other part, you can choose the subtitles you want to copy. In the common settings you can preset your favorite subtitles. The ripper provides a column called "subtitles". There you will find a drop down menu. One option is called "Display only forced subtitles". If you deselect all preset options and select the "Display only forced subtitles" option, I think this may do the trick for you.