Just be sure that when he calls, he calls the hotel direct and specifically askes to talk to IN HOUSE reservations. Otherwise they'll shuttle you to the national reservation line, where they don't know what you're talking about and can't give you the Ent rate.
Also, you don't need to purchase the whole book if you don't want it; you can buy just the card on e-bay for a few bucks.
Make sure you get someone IN HOUSE, the national reservations people are clueless and are rude! You need to call the hotel directly and don't just say I would like to make a reservation because you will then be transferred to the national people, make sure to ask for in-house.