A quick alternative -

Print your image on a normal easel. Place a mask cut to just smaller than the image size on the paper and use weights or magnets at the corners to keep it flat and aligned (as if you were going to do a pinline border). Lift the easel frame. Flash.

The mask being smaller than the image prevents you ending up with any white paper showing between the image and the black border. The approach saves you an exposure, but you may lose time aligning the mask.

Best of luck with whatever approach you use.

Frank