From what I've heard, most of the "name" postbac programs are done with their classes, with all new interviewees and previous holds moving to the waitlist. Most schools are going to have some sort of order to their list, that they're going to use. It's very unlikely that you'll have any influence on this, but writing a letter of intent or something like that wouldn't hurt. I heard postbac applications were up 20% this year, making it a bit more competitive than past years.