As far as I know, isotrim is not capable of this. I would try to reduce the problem from a surface to a line. Take the top and bottom edge of your surface and play around with the curve division, divide by length and evaluate curve components. Shatter your lines and piece them back together according to your needs. When you have the correct division points of your top and bottom surface edge, you can turn points back into lines and back into the surface. Interesting problem!