cc_load_policy (supported players: AS3, AS2) Values: 1. Default is based on user preference. Setting to 1 will cause closed captions to be shown by default, even if the user has turned captions off.
Unfortunately I don't think this is possible as it's a user-preference. The cc_load_policy refers to disabling/enabling the toggle button for the player (limited to AS3, AS2 players). And since VideoJS is based off HTML5, I'm imagining the cc_load_policy isn't available for your use either.