Check out my Rhythmbox plugin, rbpitch for changing the pitch/tempo/speed of the playing song. I know it's a hack, and you'll have to manually work out the correct tempo to set to get it to flash in sync with your cursor, but for this extremely important and practical task, I thought it would be important to give you a temporary workaround until someone figures out how to work a gstreamer pipeline using the beat detection plugin into bash or whatever virtual terminal you're using.
You know, now that you mention it, doing this wouldn't be all that extremely hard, and I could probably code it up in about a day using SoundTouch's BPMDetect class.
Stop giving me ideas for how to look busy coding while actually wasting time.