The Luthor-Clark clonebaby thing was Geoff Johns' retcon in Teen Titans. Here, Kon's DNA was still based on Paul Westfield, the former director of Project Cadmus. (Westfield was an ass, Kon wasn't happy when he found out his heritage.)
Oh yeah, and the first time the Luthor-Clark thing was mentioned? In the letters pages of the Superboy ongoing, suggested by one Geoffrey Johns. It's possibly it's not the writer of TT who later made the idea canon, but it's a heck of a coincidence.