Just spoke with a Hertz agent he told me that by showing the Gold Member Card, the additional driver can waive the underage fees too. I think I'll risk it and prepay online. If this thing with the additional driver won't work, then we'll have to pay the fees at the counter in NY. Alamo under 25 special- gives the same rates for me with additional driver fees included and underage fees for both drivers. At Hertz I'll have at least the chance I won't need to pay those fees!

Thanks for the help :-)