How can I repair pinstripe trousers diagonally frayed at seat ?

Is it possible to repair a pair of men's vertically pinstriped dress trousers which have become frayed diagonally at the seat? I have thought of trying to darn and then using iron on vilene stiffener, but do not want the repairs to be visable. Please help. I have no spare matching fabric to use and I need for the repair to stand up to being able to be worn without causing embarassment to the owner of the garment. Not sure it would be possible to darn them without creating unslightly tucks in the fabric?