You have to use the Amex CDP
No need to change anything.
To get the Hertz/Amex relationship you have to use the Amex CDP.
There is no stacking.
Just like you can't use AAA and you corporate contract, same with this.
But if you use the Amex CDP you will see the waiver.
Just did a rental that was 4 days with AAA (pick up at 10AM, Return at 2PM), but was only 3 days with Amex code.