My school has rather the same problem with the anti Greek mentality. I suggest maybe having a table out somewhere central like a Student Union or bookstore that first week ...have out a scrapbook/mascot/any other paraphanalia that you can think of and just talk to people to get the word out. Hand out fliers and answer people's questions when they come to the table, if they are interested, you can get their contact info and E mail to remind them. It can be intimidating to do this, especially at a school where you're likely to get responses from eye rolling to people loudly saying in a false bubbly tone to their friend as they walk by "OH MY GOD TOTALLY JOIN LIKE MY SOROITY" BUT on a campus where people just don't "GO GREEK" it's the only way people may even know you actually even have a greek system. We only have one table since our campus is rather small.. NYU is HUGE so if you can have two or three tables at different places around campus that would be even better. Also wear letters/jewelry EVERYWHERE the week before recruitment starts. I would also do you best whenever you get the chance to dispell any rumors you hear about GLOs around campus... I know at our school a lot of people think you get hazed.. so whenever I get the opportunity I try and make the truth known.
I have visited NYU.. though I'm not a student so don't know how well these ideas might work on your campus.. but the general idea is get the word out any way possible.