I don't think it will be too much, send another essay or may be an update on your clinical experiences, anything that can help them to know you are truly interested in the field of medicine and their university in particular. I was shadowing a doctor recently who happens to be an interviewer in one of the medical schools in Florida, he said they have their ranking system in that school, but they won't tell the applicants about it. May be it's different from school to school. Anyways, you still have good chances to get in out of all three wait lists. Fingers crossed for you! By the way, I have been waiting for 6 weeks now, and it was the only interview for me, don't have a good feeling...