Tie a small washer or other small weight to some sewing thread or thin string. Hold the wing vertically, feed the weight from the servo pocket into the wing panel and slowly lower the weight, holding on to the other end of the thread. With a little fiddling it should make its way to the spot where the servo wire is supposed to exit the wing. Grab the weight with a pair of tweezers or forceps, pull it out of the wing and you have a new string to pull the servo wire with.