I think this is something that you need to plan for when you capture. Normally, unless you tell it different, FCP captures video and audio as one file, so trying to consolidate JUST the audio is something that it might not be able to do.
But, you can tell FCP to capture the audio and video files separately. In that case, I am sure than media managing just the audio would be a snap.
But I haven’t tried it, so…I cannot say for sure.