Here is the conversation that took place at WB Studios that led to this casting choice.
Assistant: Sir, the fans and the internet are all clamoring for Heisenberg to be Lex Luthor...
WB Exec: Well, what do you think of that choice?
Asst.: frankly I think it would be a great fit.
WB Exec: Then I'll have the casting director get him in here to audition for the part.
::several weeks and phone calls later::
WB Exec: Thank you for joining us Mr. Heisenberg
Jesse: It's Eisenberg sir
WB Exec: Yeah, right, I haven't seen it myself, but my daughter was huge fan of your show Breaking Bad...
Jesse: That's Heisenberg sir
WB Exec: That's what I said
Jesse: But I'm Eisenberg sir
WB Exec: That's close enough for me, you got the part.
Jesse: ....