No one is allowed to talk or hint to a player.... (rule 1.6.1) .... time-out .... may be called by the player or the captain.... (rule 1.6.2).
Team members other than the captain are not allowed to call "timeout"; asking the captain to call a time-out in a way the player can hear it may be seen as hinting to the player and may be treated as foul. However, I don't see a reason why hinting to the captain to call a time-out should not be allowed, as long as the player is not hinted at the same time.