What kills me is that I like to leave a black pin border from my full frame images and it's too precise for that method.
I recently saw a method to that; so I am going to try it soon.
The method I saw was having a piece of rigid black material, plastic or steel. The piece was about 1/8 inch smaller all around than the easel opening. The idea is to make the exposure as normal then place the piece of black plastic on top of the print being sure to center it evenly all around; then exposure again for long enough to give a black border.