Cutting a coil off the spring isn't really good practice John as this would have an effect on the springs travel when the car's weight is off of that wheel, going over hump back bridges and the like.
Suggest to you customer a single coil compressions, by this I mean remove the spring and heat the lower section to squeeze the bottom coils together, it'll keep overall strength in the spring and lower the car. Very important though, don't quench it cold with water, let it cool in a none drafty environment otherwise it could snap!

Hope this helps
