AFAIK the cars used by professional driving instructors have a brake that can be manually operated by the guy seating to the right of the driver. First of all, where do they get such cars nowadays?
Second, why isn’t it possible to buy or rent an easy-to-install gadget to add this feature to any random car? If, hypothetically, I were to make and sell a gadget that would basically mess with the behavior of the “brake” and “gas” pedals to achieve that, would that be legal or are there strict rules about this sort of controls modifications?