P: Fill in empty areas in transformed or cropped/rotated image

Particularly with architectural images it is useful to transform the image to make building edges vertical or horizontal.   This leaves the image in an odd shape with missing corners that need to be cropped - or perhaps small corners that could be patched up with the clone tool.  However, the clone tool does not work in this case because these areas are outside of the original image.

Why can't Lightroom fill in these blank areas with some added pixels so that this subsequent editing can be done within LR?