Locked in his heart
The moment Lex returned to the Inn, he teleported away to his room. He placed the teacup aside, somewhere where he wouldn't accidentally use it to drink something from, and began perusing the method to induce the affinity.
It was complicated, to say the least. Firstly, the method would work best on someone who was building the foundation. That made sense, since if the foundation could be influenced, then when the golden core is formed the affinity would become more evident. During the foundation realm the affinity would merely begin to show its influence.