I need to print about 60 images for an exhibition, and rather than matting in black I want to print the whole paper area black, aside from the photo in the center. I've attached a couple of jpegs below to illustrate what I'm looking for. Most of the images will be square, but a few are wide.

I'm not looking for black lines, but black paper background.

Any ideas for the easiest way to achieve this effect in the darkroom?