well, i was reading between the lines a little too loosely, I guess. I read that you actually tried to use it online and it wasn't showing up for you. if that was the case, calling to a human would be the way to go. if you didn't actually try it and were just asking, sorry, my bad.

You can just do a normal rewards search and if the hotel you choose is a cat 1-4, the promo cert shows up pre-selected instead of an e-cert. (which you can select to override the promo cert).