This season the ACC did away with divisions and the two teams with the best winning percentages play in the ACC Championship game. Why not keep that format going forward, but with a 7-game conference schedule minimum with the proviso that you must play every ACC team once every two years. ND could thus play 7 conference games and still have 5 out of conference games against USC, Alabama, Michigan, etc.
Some teams like North Carolina might play 9-conference games in order to play in-state schools Duke, Wake Forest and NC-State every year plus still meet the requirement of playing every ACC school once every two years. Some schools might play only 8-conference games. Since the two teams in the conference championship is based on winning percentage, it is not necessary for each school to play the same number of conference games.
In order to get ND into the football conference, I am willing to bet that not only would the ACC jump at this, but they would also let ND keep the NBC contract going forward.