I guess it depends what you're trying to do which upon further contemplation would be to retain the use of the camera and mic when you want to but disable them at all other times. I would say that if you're that concerned to cover the camera then the microphone should be deemed a greater threat. Audio might not give as much info but it would always be available. And once you're at that train of thought, then what about integrated GPS? Sure, any cellphone could be triangulated via cell towers but GPS would be quicker and more precise.
Obviously you want to still be able to use it, receive calls, etc. so no faraday bag or removal of battery (if that's even an option). Maybe you could open it up, give the camera and mic individually wired switches, and disguise it all by making a neat replacement case (steampunk, hardwood, Star Trek PADD, etc.).