If you want somebody to play a full 48 minutes, you need to use "Strictly follow depth chart." Still, if you use a blank lineup, they might get substituted out. The safest way to get 48 minutes at one position is to use the following format while dressing exactly 9 players and leaving all others in the "remaining roster".
(Position: Starter, Back-up, Reserve)
PG: Player A, Player E, Player E
SG: Player B, Player F, Player F
SF: Player C, Player G, Player G
PF: Player D, Player H, Player H
C: trainee, trainee, trainee