Start a season in January (if that option is/was ever available, but I seem to remember it being there) and disable transfers for the first transfer window.
Holiday the rest of the season. Then once the season is over in the league you want to join, add a new manager and take over the club you want and retire the other manager.
If I'm going mad and the option to start in January is a figment of my imagination, disable transfers for the first window and holiday till the end of the season, but just accept that the AI will buy in January.