I am just over the mountain at East Tennessee State University.... I know that one of your sororities has a chapter here. Perhaps ask nearby chapters from the two organizations to come in for a big spirit weekend or something before you start recruiting. If you can double your numbers by bringing in sisters from neighboring universities, that's a start and will make you more noticeable on campus.
Another thought is to enist the help of boys. This is walking a fine line, as NPC expressly forbids the use of men during recruitment, but you can use them beforehand and work together to increase their numbers as well. Get a Greek system-wide tshirt that screams "GO GREEK" with everyone's letters that everyone, no matter their affiliation, will get. Have buttons made. Since you only have two sororities, you can afford to even get the buttons that say "I heart AZD" and "I heard GPhiB" and have boys stick both on their backpacks.
Order the exact same bumper sticker for every person in each chapter. I love those colorful round ones with polka dots and just the name of the chapter. When students see them over and over again, it just sticks with them and will perhaps induce curiosity. Like these....
http://www.greekgear.com/rosobust.html
Ask the coordinator for incoming freshman orientation if you can make a presentation at their sessions. Or at the very least if you can place an informational flyer in their packets. Our university's housing director will allow us to give flyers to the RAs of the freshman dorm and they leave them on the beds of the women.
We've tried a lot of things around here, tons have worked - a few haven't! I'm happy to continue with you via email or PM since I've created an awfully long post.