You can just get a thin piece of something strong like diamond plate or even oak.. the short Shank will till be long enough to work with this.. the curved spacer comes off the shank which gives you more wiggle room.
Or you can buy shanks in all different lengths. As mentioned you don't want to mount them in drywall... Keep in mind that if you don't have a cooling system for the beer lines they will foam on ever first pour or two.. I learned this that hard way myself..= a lot of wasted beer if tou only use it for a beer or two at a time. Most wall mounted taps have the walk in cooler directly on the other side of the wall or use a glycol beerline chiller for this reason.