The most difficult thing is making some kind of box that will give even illumination. You can flash the film from across the room but that might not always be repeatable, but it certainly is a good way to get an even exposure across the stepwedge.

These little "contact printers" usually go for little money on ebay. You could mount the flash inside one of those.
http://www.ebay.com/itm/Vintage-Aire...item2ec1b84559