This entire procedure would likely be made more smooth if you could coordinate by cell phone, but should be possible even without, and can be pre-arranged before arriving at the airport, or even knowing the airport layout.
Have your friend drop you off at the customer-drop of section of the airport, near the car rentals. Instruct your friend to exit the airport, as usual, then re-enter the customer drop-off area and watch for you at the same spot.
You go inside, get the keys, etc, and go pick up your car.
Drive your rental car to the customer drop-off area of the airport where your friend dropped you off. Get out of the car and stand next to it and wait for your friend. As long as you are there less than a few minutes, this is usually permitted.
When your friend comes back around, have him pull up near you, transfer your belongings, and be on your way.
On your way to the airport with your friend, keep your eyes open for a good spot to do the exchange, and agree to meet there immediately after he drops you off and you pick up the rental car. Look for a public parking lot, or even just a wide shoulder, which will be easy to access, and free.
Use the Hertz customer parking. In some airports it may not be obvious where this is (and it may not be convenient), but every car rental agency ought to have public customer parking. You can always call ahead to ask where it is.