Due to the vast amount of time between now & then, you can just make up gods for Joseph.
Example:
Perhaps the Mormons flew off and were isolated from the galaxy for 200 years. They showed back up as a cult named "The Greater Mormon Church of the Revered" and started doing door-to-door religion selling. Peopl kept calling them Mormons but they kept saying they were Greater blah blah blah. People love to shorten things, so by 500 years ago, people just called them "The Greats" or "The Greater Church"
The Greats teach there was a second ark (this guy can bear the brunt of the Moses jokes). They teach in a garden of Eden they found on their homeworld (here go the Eden jokes). They believe in 4 gods, including one called "Baba Yaga" whose "Book of Life" has chapters and verses very similar to our own and are held sacrosanct by a population grasping for meaning after a deadly virus almost wiped them out.
--End example--
If you write such a thing carefully enough and have enough religious characters to carry the reverence, then you can make it work without touching Christianity.
(Note: This advice is coming from a guy whose characters worship the stars.And I still squeezed in a concept of ghosts, ghouls, and vampires. My world left religion behind, but I'm careful to throw in the occasional old altar that people hope is good luck. When I wrote the Pearly Gates scene and the Angel of Death (Victorious Chapter 13) I carefully stepped around the word God or Heaven or Astral Travel by renaming them. I could be irreverent with Sara-Kael by getting him beaten up. No reviews came in "I really don't think you can treat an arch angel this way" or "It's unholy to climb the pearly gates")
They key element is to remember to have 80% of the cast respect it (even if they don't actively practice). This is one of the few areas that Babylon 5 dropped the ball. The Vorlons should have been much more respected once the big reveal came of what they were. When the second Kosh showed up, how come there weren't crowds of people waiting to bow? I think ir was one guy. Anyway, you need the people to get offended if Joseph says "By Baba Yaga's beard!"