At this time, there isn't a setting to set the Audio File to play once (unless you add it as an object - but then it will not play through the entire lyric cue). The only option to manipulate this to work for you would be to set the lyric cue to automatically advance after that audio file finishes playing. I would have it auto-advance into just a blank page with the same background as the lyric cue had. Then, you can sit on the blank cue for as long as you need before going into the rest of your presentation. Would this work for your situation?
We have the Developers working on adding this as an option for Video/Audio files, but it is not yet ready. I apologize for that.