One way I can see them rebooting but keeping Cavill is having him doing a voice over a montage of him growing up, showing new parents, Lana and Pete, talking about how his parents raised him to be the man he is today, mention he works at the Daily planet with Lois who is also recast, show him doing simple heroic acts (and engaging with the people he is saving..for example talking), show him doing big world heroics and then bring him to the present where he is being interviewed by Lois... Which is what parts of the narration are and carry on from there.