I think I may have stumbled upon a way to save the debit card fee on the Chase CO card when doing the 25,000 CO miles deal.
My card never came in the mail so I called and asked for a replacement. They sent me a replacement, and I didn't even realize they sent me a standard debit card instead of the CO debit card. I made the five purchases and low and behold, the miles still posted (all but the last 2,500 which I heard posts later). I called and asked Chase what kind of card I have for that account and they said a no-annual fee standard debit card.
It could be it was a fluke and if people try and switch the debit card they won't get the miles and will have no recourse, but it might be worth a shot. When do they usually charge you for the debit card annual fee? Couldn't you downgrade after the CO miles post?