I don't have to do this now I have shrunk to a 38 inch waist from a 50 inch equator, but I have used a toning plain fabric for the under apron and associated large pleats so as to get enough fabric for the small pleats and apron.

I did consider making the apron pleats on both sides from the toning fabric, so it looked more deliberate design rather than desperation, but have never got around to making that particular kilt.