So I actually almost applied to Emory and ran into this same issue. They do have different requirements for their letters, don't they? I scheduled a time to speak with the program director and kinda gave her an elevator pitch of the things I have been involved in. From our quick conversation she was able to identify someone else that would be a suitable reference and was going to make a note in my file. I didn't end up applying there for other reasons, but don't let that requirement deter you if you are really interested! Most schools would be willing to work with you on that sort of thing. Who wants to be a cookie cutter applicant, anyway?? good luck!