Thanks for the info, everyone. I just got off the phone with DL and the guy said he could not change it -- hard as he tried -- because, while he could waive the fee, it was asking for an additional 50,000 miles per ticket (100k vs. 150k level). Very frustrating but he said, "have patience and just keep calling back every 3-4 days and I am 100% certain the inventory will open up."
Should I just try back later tonight and see if I can get another person who can help, make an exception, etc?