Let me pull the doc and look into this.
After reviewing all the documentation, i find that it is not possible to do with that model. It is possible to take a photo still while shooting a video with audio (that will only grab a frame of the same resolution of the video and not use the max resolution possible of the camera). That said this allow to have a real time sound sample of the scene you took as a still.
It is not possible to just record audio only either, so if you want to have an audio track to later (on your computer editing station) mix with the still picture, you can cover the lenses and shoot a video and use the audio part of that video. Covering the lenses will allow the picture to stay black and take the minimum space on the memory card so it take barely much than a typical mp3 file. The sound will then need to be recorder before or after taking the pic and not "while" taking it as possible with the frame video grab technique explained earlier.