http://www.flyertalk.com/forum/hertz...-plat-cdp.html
Centurion might be different from Platinum but I wouldn't have thought so...
You can sometimes use PCs such as 192021 to bring down the flexible rate (it gives you a free day on a full size or larger when you take a weekly or longer rental). Usually it just means that the flexible and prepaid rates are close.
In Europe, I've never managed even that.
RQs are somewhat different but they rarely work for European travellers because they kill the included insurance and have to be booked through the US site, at least in my experience.