This won't help you for scratching, but there is a mode in MixEmergency that lets you use your records to fade the video. To use this, go into MixEmergency's preferences and select "Stopping media triggers Auto-fade" from the Transition section. Once this is enabled, pulling back or stopping one record (as long as the other record is playing) will cause the auto-fade to be triggered towards the side that is still playing.
