You could also "Conform" the footage to 29.97p in Apple's Cinema Tools. That would change the audio sample rate and require FCP to convert the sample rate in the timeline. To me it's better to manipulate the audio rather than the video.

You could also process the audio separately from the video by making AIFFs from the original video file and just remember to remove an audio frame every 30 seconds to keep it in sync. A dropped frame in video is usually obvious, not so with audio if it is chosen carefully.

Given shots are typically 20- to 30-seconds long -- this should not be a major issue. These shots are then trimmed to 5- to 10-seconds.