Hey... why not just take a standard swimbait (like a generic one or a Hurricane shad, the ones with a flattened, tapered belly) and rig it so that it is sideways in the water? You could put the hook in the squared-off "nose," but put the point out where the pectoral fin would be on a real fish. You can buy these baits in every color imaginable, but-to be as natural as possible- should match the sand on the bottom, as Flounder change color to coordinate with their color. Light sand, a regular yellow or white lure would work, but on dark sand, you could paint one side of the lure and seal it up with, like, epoxy or something. Some lures even come in a translucent color, that when charged up with a flashlight, will give a weak, but visible glow for about 30 mins.
Hope this helps.
><> ><> ><> ><> ><>-------------------o----------