To go along with Jen's suggestion, you could handed roses to your mothers and other family memebers.
or, I know this is not tradition, but since you will have all that extra time, you could have the mothers wait until the ceremony to light the unity candles.
So when it is time to light the candle, the music will play, the mothers will go and light their candles, will take a moment to take it all in, will walk back to their seats, then after a moment, you and your fiance/husband will walk over and then light the actual unity candel (with music still playing).
Does that make sence?
You may still have a while longer to wait till the end of the song, but at least that process will take up some time.
or you could just do it the traditional way, and have the music stop when the unity candle lighting is over, and then have the remainder of the song played while your gueasts are leaving.
That way you still get to hear the whole song, but wont be stading in awkwardness.
Just a suggestion!