Having pleated some fabrics which might be considered strange - one is pleated to the goldfish, I do spend time in experimenting to get the best effect and do end up with pleats which are neither to the stripe nor to the set if analysed strictly, but I like to think that they are all at least giving a nod to accepted methods of pleating.

With a large set in a heavy fabric a box pleat might be an option, as might pleats of irregular size to give the illusion of pleating to the set - even if it is not an exact representation something close could well fool the casual observer.

With such a large set there might well be more hit and miss scenarios depending on just where on the set the fabric was cut.
I had two kilts which had to be made differently even though they were the two halves of the same bit of fabric. There was damage on one half just a few inches from the edge but whilst the other half could be used as it was, with the folds falling exactly right removing those few inches threw everything off. I even thought of turning the fabric upside down and retaining the damaged part, mending it and using it as the under apron. In the end I recalculated and made a narrower apron and a couple of cheats.

Having considered that the kilt is already made, and the pleats cut, more than likely - perhaps the kindest thing would be to sell the kilt you have and set your kilt maker the problem just of creating a kilt of the correct size from whole cloth.

Anne the Pleater