If you don't put it on the back of the bow, it's not a backing. The back of a bow is under tension load, the belly is under compression. The purpose of a backing is to keep the bow from failing in tension, i.e. to keep the back from breaking. If your boards have good grain and are tillered well, they may not need a backing. If you're asking about putting a purely cosmetic backing that isn't adding tension strength on the belly as well as the back, it should work as long as the compression doesn't loosen it.