Use this link and select Ambassador Certificate for the rate preference.

http://www.ihg.com/hotels/us/en/rese...eference=IBAMB

You'll probably have to chop your stay up into a few different bookings and ask for them to be linked as it's not letting you book a Thur - Tue, but does let you try a Fri - Tue on the AMB rate, so you just book the Thur night on its own.

If you book a business king room from 9-11 Sep for example, it's $317 a night roughly, you get the 2nd night price free, so you need to work out the best combination to make the most saving from it, combined with the extra benefits you'll receive whilst there. If you Book Fri - Tue on this rate, you still get the 2nd day free.

Factor in a 6 week delay to receive the free night cert though, you need the physical bit of paper when you check in.