Reprogram the ECM, that’s what the “cheat” did, one mode for driving, another for testing.
The engineers figured out that when a car was on a dyno being tested, there was no steering input. That is what they used to switch the program.
I have a Duramax with a similar Bosch common rail fuel system. I added a switchable performance modification. I have 5 different programs I can run and you can switch them on the go. Overall, still partial to the old mechanical P-Pump.
A lot of these will be reprogrammed by the dealers, then re-reprogrammed by the owners......................