Or maybe not exactly a surgery. Maybe (brace yourself, this might hurt)...It goes without saying that he (Sybok/Michael) has to have gotten a sex change, race change, and species change, since he's constantly referred to as Vulcan, maybe to the point of an Ash Tyler-esque surgery.
Michael discovers mind transfer technology, and to hide from her past, steals the identity of an innocent scientist named Janice Lester. All she has ever wanted was to command her own starship and get close to Spock. After the Kirk operation failed, she transferred to Sybok for a second attempt. Spock was the only one who knew the truth.
Can this theory get any worse?