I have seen these in my local Wicks. I can't remember if they were singles, doubles or both. Also I think they stuck out a little more then a regulare socket (but not much more). I remember them, cus when I saw them I thought "oh I could do with some of them".
Although do you know of anything that could integrate with an existing faceplate as I am a bit of a ponce when it comes to aesthetics and would prefer to keep my brushed steel plates