That doesn't sound like it should be possible. It's fairly trivial to put an application in a sandbox where it can't make certain system calls even if it wants to. If iOS doesn't or worse can't do that, that's a design flaw in the OS. Making them pinky swear to get listed in the official app store isn't real security. What the heck way other than through the OS can you ask for access to hardware? That's the entire point of an OS. Ability to prevent hardware access shouldn't depend on the distribution channel.