Here's what I did. I edited the rosters to remove all the best players from each team over 84 overall before starting the franchise mode. I moved them all into free agency.
I then added low quality players from other leagues to limit teams from having room from adding contracts but I don't think that step is necessary. Won the cup without playing any games. You just sign all the best free agents who will be all the superstars you moved into free agency in roster editing before starting.