Good question. If you just need 1/2″ you could stack the spacers. But, that can be a little tricky. What most people do is use a piece of foam board as a shim, lay it under the lip of the frame all around the frame and then use double sided-tape to put mat board (if a black frame, a black mat board would not even look like anything other than the frame) on top of it. So, you are putting the shim or foam board vertical along the inside of the frame sides. Does that make sense? Hope it helps. Thank you.