I agree with stu. I've never heard of such a thing... but if you can come up with something and it works.. go for it... maybe make a buck. So you'd mount them outboard, like a big truck's side view mirrors, right? Maybe make them remote controlled? Hmm, interesting.
Rather than do that, as Stu suggests, I'd try steering from the side of the wheel, instead of standing directly behind it. Going down wind it's not an issue, but going up wind, close reaching, where you're normally steering by the telltales, it's best to sit to the side. One of the great advantages of tiller equipped boats is that a simple extension allows you to sit on the rail with the rest of the crew while you steer and keep an eye on the telltales. A wheel in the cockpit, especially a small one, is pretty restrictive for steering position options. That's why you see those giant destroyer type wheels being installed on many boats. It allows the driver to move from side to side. You even see alot of dual wheel equipped production boats now... but your idea is a much cheaper upgrade.
So, KandD, even though I've never heard of such a thing... I think it's an interesting idea that could be easliy implemented. Just buy some side view mirrors and clamp them on the pulpit rail. A simple solution to the driver that likes to stay in the middle of the boat. Give it a try and keep us updated.