Thank you so much for this information.
I'm dealing with this exact problem at the moment. It will be a plain coloured wool or drill kilt (thankfully no plaid to worry about) I haven't cut anything at the moment. I had used the search function and learnt about "gut cut" and other terms but I wasn't happy with that solution as it would look awful on the gentleman. I'm waiting to get hold of him for a new set of measurements and I shall use this method. (Hopefully I can convince him to wear it at his waist not at his jeans waist)

Extra question... Is this method suitable for a more casual a box pleat kilt as well?