Take a look at this league. You may want to contact the commish and see how he does it.
United States Baseball Association | An OOTP 15 Promotion/Relegation League
Hey all, I am the commissioner of the United States Baseball Association. We run a three-league promotion/relegation system consisting of thirty-two teams. We have an extremely active core group of about 10-15 managers at all levels who are on AIM. We have very lively and engaged discussions. We also have like 10 more guys who export and respond to their emails on a regular basis. League participation is great. Every year is overwhelmingly better than the last. The sky is the limit for this league. We regularly have 5+ of 10 clubs at each level in contention for a championship or promotion.
Features unique to the league include:
--In-season League Cup (think FA Cup in English football)
--MTWTF sim, 1 game series per sim
--Games are LIVE SIM. 3 games per team a day. You can watch your team play.
--108 game season, each team plays the other over four series (2h, 2a)
--Promotion and relegation playoffs at the end of the season
--Cash-based financial system
--GMs have complete discretion over most revenue flows
--Player loans
--Draft pick trading
--Regular podcasts and articles by various members of the league
--Non-PL Teams allowed to relocate after 1 year in the league if they choose.
--International Baseball every other off season
World Cup every 4 years teams drawn into random groups
Confederations Cups in the intermediate years.