May be some very devoted music fan can some day make a difference...
Sue them under false advertisement. This is not the persons voice as depicted on the cover, this is a computer generated voice basing on the person's voice. Then, after one or a few such law suits, the record company may find it necessary to put some visible indication on the cover; something like "This recording has been modified by computer and is not a true representation of the person's singing."
Law suits are expensive, so this will need to be a class-action kind of suit driven by a group of some sort. Seriously, I would consider joining such a group. I am not particularly devoted, but I like my music real. At times, the imperfection or even the trembling of the voice can convey real emotion adding to the singing.