Hi Allen,
Welcome to SimplyDiscus.com! Your Idea is worth giving a try, but generally most Discus Hobbyists that keep a bare tank depend on water changes to remove the wastes like Nitrates... thats not to say that a refugium would not be of a benefit... it could be of great help in water purity..just be sure not to rely on it in lieu of water changes... especially if you are growing out young fish being fed alot and often. Keep us posted if you go that route..
Some of us use a semi-refugium idea.. Hanging plants like pothos and philodendrons can soak up some of the wastes..others use a bare tank with potted plants...so all variations on the same theme.
Hth,
al