A cure!?
Unfortunately, no. If there were to be a cure for Klinefelter's Syndrome, or any chromosome disorder, all the cells in the body would have to be fixed by removing the extra X chromosome, which is impossible currently, and it could even remain so into the future. However, there is help for those suffering with this disorder.
Treatment
If this disorder makes the afflicted have more characteristics of a female, then it makes sense to have testosterone as treatment in this case. Testosterone will be applied to help reduce some effects such as speech impediments and learning disabilities. This treatment is best started during the puberty phase of a person's lifetime.