For a considerably less permanent rear fender option, you can secure your wire to a piece of spring steel with little pieces of heat shrink tubing every few inches and mount that under the fender. You have to bend hooks or eyelets into both ends of the spring, which is tricky since spring steel doesn't take bends very well. Get it right the first time and you'll be okay; try to bend it a second time, and it will probably break. If you need two wires, the spring can probably serve as one of them. You will find a piece of spring steel, much longer than you need, in the bead of an old tire.