I'll just add the quick point that in my opinion, it's ideal to have 8 rather than 9 players if you're going to have a risk of garbage time, since if one of your non-trainee starters is going to shoot free throws when the coach decides to empty the bench, that player's backup will then replace your trainee, while there's a chance otherwise that he'll replace the other guy instead. Even better would be seven, with each of the two backups covering two positions, so both will have a player to replace regardless of free throws.
And then you'll end up being in a close game and having your trainee with 5 fouls start the foul parade with a minute left.