The short answer for you is you are hosed.
Stillen now says the support rods are required. Run without at your own risk. I bought my lip from a vendor so it was likely old stock. According to Stillen they now apparently put the support rods in as part of the kit.
Here is what Stillen had to say back in April.
I recently bought this lip after full well knowing about the sagging issues others are having with it. However there is another fix, that likely wont help you at this point, that doesn't require the support rods to keep the clean look. It uses another form of support but you must do it prior to ever installling it or at least prior to having issues with the lip itself. Buy a piece of aluminum L-bar stock at your local hardware store. Fit it over the lenght of the middle section of the lip. Use 100% polyurethane adhesive to attach the bar to the lip for added rigidity. Then mount it to the bumper securely.
Another member has done this method and hasn't had any issues of it bending or sagging many months after install and going through the elements. This convinced me if you are willing to spend $30 more in hardware and adhesive (you gotta buy better hardware to mount anyway). Then doing the little DIY project of installing the bar for support then the Stillen lip may still be worth considering. I really like the way it looks. The only others I like are the Top Secret and Mines. Or the Sunline Racing if doing the full lip kit. But even after buying the extra hardware you come in way less than these and still have a nice look.