so i dont know how the lumia 800 does this. i assume that you want to do this while inside the camera app; press and hold vol+, wait 1s for it to focus, release to snap picture.

totally feasible, except for the focusing bit. the built-in camera doesnt expose any way to forcibly make it focus {that i know about}. one could easily just write another camera application for doing this with qt mobility, but it wouldnt be as full-featured or polished.