Attach a piece of wire to your camera. Bend a rectangle corresponding exactly to the framing at the extension and magnification your want. You'll have to mess with it quite a bit to get it right. It will be like a wire frame viewfinder out in front of the camera that is in the plane of focus, and exactly in focus. Now, the harder part; bend it it fit round your face so your eye is just where the focus is. I can't see how you'll do this without some other person to check focus, but maybe you can fins a way. Once you have all that, you could then work single handed and do the photograph you describe.