I find the key is to have a copy of the character sheet in front of you, and roll spot checks and such for them. That way, you don't say "Sir Knightley McScotstabber, make a fortitude save!" "What!?! Why!!!" "Oh, no reason."
Instead, for things that need to be kept secret, like spot checks, search checks, poisons, forgery checks, sense motive, disease, those sort of things, you roll for them yourself.