My first thought was also using two images in photoshop. Maybe you need to do the computer work at home, and do a real nice job so they then buy you the right stuff? I would suspect though that you could crank up the ambient lighting enough to equalize the case with the display. Tricky. Nice to set everything up using a digital or polaroid, then go to your film. Could also maybe try a double exposure; expose for the display, then pull the plug and expose for the case? Again tricky.