Not the nominator, but in Machineries of Empire, all three of the nommed characters use(/have had used on them) an immortality process in which they become kind of shadow creatures (living a disembodied existence in something called "the black cradle") that can be attached to an "anchor" human. Given the books tend not to overexplain the sufficiently advanced technology it's hard to know exactly how "artificial" the whole process is, but they're definitely not "100% human characters" to my way of thinking.