[he frowns at Yuuki's suggestion, but can see she's not comfortable with it either.] I would not want to be using mind or memory control, myself...
If they're not on the Force, and they haven't used violence or threats, I'm not sure there's much to be done other than warn them. I should hope anyone who volunteers for the task force would be willing to agree to such, either because they have something to lose or because they joined in good faith.
If a non-task force member were to reveal a vampire, I should think the official, and public, disapproval of the Defense Force and task force would go a long way toward good will. That may have to be enough. [if they start trying to police what non-members can or can't say, it may not end well...]