I do it in the private league each week. Works ok but less control over minutes. If you only have 1 or 2 trainees I guess you would just name them in their spots and leave the rest clear.
I've tried that too but they are immediately substituted with "let coach decide". And if you set "strictly follow" and you have blank spots, some weird rotations can happen and trainee gets 3 quarters and gets substituted in the fourth.