One workaround: Take the pencil tool and insert to 2 opposite corners 1px shape, have pencil opacity=1% Of course this isn't exact, but it can be usable. Maybe you can later delete those 2 extra pixels, when you are in another application.
You do not need any extra pixels, if you in the layers panel close all but the one layer that you want to export and save the image as PNG. That PNG has size = the original image size.