From what I have gathered, you have to send your supplemental docs to Kim Szpiro at
kas396@cornell.edu.
If waitlisted you would have received a generic email about 2 or 3 timea as to how you can enhance your profile. If its gmat try retaking it, and if its gpa, take the mba math foundation course on coursera and submit that grade. Try an additional lor from ur manager if earlier ones were not from him/her.
And lastly if you dont fit into any of the above, just convey ur interest at least. The beginning of this thread has a chat transcript which contains some useful answers on the waitlist related questions.
Hope this helps