AFAIK , since USB is an active connection there are no know switches for it.
What you COULD do is make your own 4 wire switch (that is ONE switch , switching four wires) that has 3 settings : setting 1 , disconnected and setting 2.
Because you can unplug USB anytime you want , it doesn't mean you can plug it back in quickly to another port. You will need to give the operating systems some time.
You can easily make this by getting some components from Radio Shack and a couple of USB extension cables.
However, i do not recommend such a thing , since you are planning to do something that is outside the scope of the USB specifications.