1. If you don't already have one, create a small lunch menu. A Thai restaurant in my town did this, and, even though it is s semiformal, sit-down type of establishment, it has gained a reputation as a place for lunch. You can even change the menu-item names to be more catchy for lunch and then go back to the formal names for dinner.
2. To increase foot traffic, you may wish to promote your establishment through venues such as discount gift-certificate site restaurant.com or a deal-of-the-day Groupon type of campaign. This route could be your chance to really wow your new customers into staying with you longer term. Also consider small advertisements or even an announcement in the local paper that you are introducing new items or menu.
A different issue may be afoot concerning your distance from offices. If your pricing can be adjusted to match the local university market, I'd bet that you can attract more lunch traffic closer to home.
Small moves here and there will give you short bursts of traffic. Then you can do your best to gain loyalty, increase it and spread positive word-of-mouth.