Just looked at the wiki page for Novac and read all of the information when it comes to each of the ending slides. It's weird why none of the endings are good outcomes. I'd love to help Novac out and get at least 1 good ending from that location. Even the best ending still gets people killed.
I have a idea, The NCR could lay claim to Novac but only if the old lady that runs the front office dies since she's like the defacto leader of Novac I guess. And most of the other people in Novac are already apart of the NCR or were apart of them. But as long as she's alive she would reject their offer to join and the other residents would join her side.