Hertz have a few bonus mile promotions going on at the moment. One such promotion is with Lufthansa Miles & More. It’s pretty simple. Instead of the standard 500 miles for a rental, if you rent for 3 days or more, you will receive 1,500 miles in your Miles & More account.
Further details are here. (I recommend using Google Chrome to translate this into English)
The promotion is good for rentals worldwide until 31 March, 2014. To take advantage of it, you need to book your car rental using PC code 194250 and CDP (discount code) 646999.