Perhaps it's time that you had a heart-to-heart with Secondary Character and told him that he IS, after all, secondary, and therefore replaceable if necessary. Depending on whether you think it will make him fall into line, you may tell him that some time in the near future, you will write a vehicle for HIM, and then he can dictate his actions with impunity. Until then, unless he wants to go on the dole, he'd better do as you say because you are The Author.