Some changes in the >1 year since the last post. Neither LHF nor THPPS30 works on the Alamo web pages (English site, I did not think to try the German site). However, I went to germanwho.com, which leads to usatogo.com, and my rental (one way, hence expensive) was 650 euros vs. over $1200 if booked directly. There is also an option to pay later, which added 30 euros and caused the price to be confirmed in USD rather than EUR, not that it matters.

This seems too good to be true...over 40% off? This is better than I ever did in the good old days of FT corporate discount code threads. (I did verify that the booking is visible on alamo.com.)