There is no salary added to payroll AFTER the BL playoffs start. So, essentially, you're giving an owner an advantage for not playing the game with an eye to the future. Game 155 is a minor addition to payroll. Very, very minor. If you don't have 4k in cap room to move a player to your BL team so he can recover, I don't feel very badly for you. Barring that, put the guy on rest the last 10 games of the minor league season. Let him recover then.
Worst case scenario, move him up when the BL season is over.
You do understand the implications of allowing owners to promote after the regular season is over with no "penalty", so to speak, right?