Dear Matt,
If you haven't already gotten clarification from the admissions director on the waitlist decision, I would try to contact him to speak with him about why they decided to waitlist you. If it is because of your employment record, then perhaps you could submit an optional essay explaining your work history or have a supervisor/co-worker write you a recommendation letter? It is best to directly address what the reservations are on your application.
Having said all of that, it is possible there is nothing you can really do and they decided to waitlist you to compare you to the next round. In that case, you just have to remain in contact periodically to reiterate your interest (while also staying positive).
Best of luck,
Lisa
