My ways...
1) Say you work as an agent for an insurance company in your area. In Colorado if you call and say you work for Progressive, or are a Progressive insured, they will rush to get you a car, and if they don't ask for the regional manger's number and they do what ever they say.

2) When walking up to the counter tell the ERAC rep you want the full insurance and they will give you the nicest car and be more then happy to help you. Then once you have done the walk around and tell the rep you've changed your mind and you'll let your credit card/insurance company cover the car.

3) Call and tell the ERAC rep thee you got a great deal from Hertz, make up a number that seems reasonable, and they will match it if not beat it.

4) Call 800-VIP-ERAC and tell them you work for such and such company and you need to make a reservation, do this a few times until you find the best rate, ask for the corporate number and make sure to use it whenever you book a reservation.