Some video cameras and a few VCRs have a feature called "audio dub." This allows you to cue a tape up to a certain spot and re-record audio on the audio track of the tape without affecting the video track. The VCRs with this feature are usually high dollar jobs. But I used to have a video camera that had this feature. It was just a common, regular priced video camera from about ten years ago. If you have a camera, check it out, or check to see if anyone else has a camera with this feature.
The best approach from an audio standpoint is still the 2 VCRs.