I hate to be stubborn, but I believe the proper method, or at least the best practice, is to remove the jacket first. If the installer damages the conductor or insulation while stripping at that point, it is due to poor practice and he is just as likely to damage it at any point in time.
I simply can't see how you can use the utility knife technique, after the cables are inserted, and be confident that the insulation is not slit also.