Another opition: JL episode Hereafter + John Carter.
Basically Hereafter but instead of going to Earth's future he actually go to another planet, with a red sun. Then just do John Carter from there, but maybe change two warring realms to a empire and it's slaves, then Clark helps free them. So actually do Hereafter+John Carter+Spartacus.
Hell, put a Dejah Thoris in it too, a warrior princess that will help and fall for Superman, but he will not get involved with her because, Lois. Hereafter+John Carter+Spartacus+For thousand years.