My battery is in the trunk as well. the only wire that's hot going into the engine compartment is the short wire going to the alternator. If you're in a wreck big enough to rip the alternator off its mount or break the engine loose, then a little #8 cable is the least of your worries.
As for cutting all circuits, I would implore you to argue that one to tech. this method cuts anything and everything that uses power or could keep the engine running. there is ONE wire going into the engine bay that's still got juice on it, and it's not going anywhere that's going to keep the car running. That's the intent of the rule, is it not?