Hmm, I know it's a little predictable, but I can't resist. Your challenge was met about 33 years before you issued it. Which I find funny since you said no time travel and I just made this all wibbley-wobbley, timey-wimey. (Seriously Steven Moffat, that's the dialogue you give to a superinteligent alien, really? I don't see Sherlock being turned into a moron by your writing.) Sorry, here's the most predictable link possible with the challenge you gave.
OK, that's probably not what you want since this is a L&C Board, not a general Superman one.
There's probably a few fanfics out on the Archive, that already have something like this. We'd have to ask the expert, IolantheAlias. Hopefully, he'll/she'll be able to recommend something for you.
Or I could write it....
Actually, I better not. I'd end up writing a thing with Superman getting a split personality disorder and going full Fight Club. Not good. 90% of humanity dead by the end and Luthor saves what's left. Kinda darker than most people would want to read I imagine.
I've rambled enough. I hope you find what you want or it get's written.
