Joe,
I have insider knowledge of this situation. Keep a few things in mind. In my state most stops are infractions (broken taillights, no turn signal, speeding, etc), not criminal, so they do not automatically give an officer the right to search or frisk you; however, this varies by state. If you are giving off suspicious behavior, though, you may get frisked.
There are a few things you can do. You can be upfront and tell the officer you carry a knife daily and have one on you, but you will keep your hands where he can see them, etc. (This is also generally recommended when carrying firearms concealed, and legally). Or, you can just say nothing and stay relaxed and don't act more nervous than you would if you weren't carrying. DO NOT MAKE ANY OBVIOUS MOVE TO HIDE IT! This will get you pulled out every time. As far as tossing it to the passenger seat, I wouldn't (would you do that with a concealed pistol?) It is still considered constructive possession, and if the officer sees the movement, out you come for a frisk.
Finally, know that some officers are more uptight than others, and they all have personal guidelines they work under as well. And, frankly, some do not know all the laws, which is understandable (there are a lot). Most I meet are adament that my state has a maximum legal length for knives, but no such law exists. Our law refers only to how a "dangerous weapon" is displayed or used.
I hear this kind of question a lot. Unfortunately, there is no one way to guarantee nothing will happen, because there are so many variable between states, agencies, and individual officers. But I hope this helps.
-Scott