You can send it to the Admissions office, to the attention of the Director of Admissions (it's on the wait list letter, if you received a paper letter?) be sure to include your applicant #.
Adam Rogers, Director of Admissions
Office of Graduate Admissions
209 E 23rd St
New York, NY 10010.
I sent one, Not sure if it helped- the only result so far was that they sent me an email that got my heart pumping, because it had the subject line "urgent message from the Office of Graduate Admissions", but turned out to be a word-for-word copy of my wait list letter. (Received on April 1st, so though I am intellectually sure it was a coincidence, a little part of me felt pranked.)
I've decided the best I can do is sit tight.