There is no easy one click way to do this. You first need to demux the A/V from the DVD. Next you need to convert the audio to wav (using HeadAC3he or other tool). Then you need to place both audio files into an audio app like Cool Edit, Audacity, etc, and make the FM broadcast sync to the original. This can be done by changing the speed of the FM, cutting very small pieces, etc.... Then recompress the audio to the same format/bitrate as the original DVD (AC3, MP2, PCM Wav, etc), then reauthor/remux the new audio with the original video.