You could try running metal straps (as heavy as you want) between the studs and screw them into the studs. Then tie into the metal strap. Paint it the same color as the wall.
If you don't like that idea, then use wood instead (1x4"). Paint it, decorate it, or stain it to match the rest of the wood work.
If you don't like that idea, then cut out a piece of the drywall from the center of each stud for 4". Then install a 2x6 backer between the studs (slid in upwards at an angle and then slid down so it is centered in the hole so the board will be behind and support each horizontal seam, either toe nailing or toe screwing the backer into the studs and screw the drywall into the board at the seams. It may help to screw a handle on the board to help get it in and then remove the handle. Then screw or nail the drywall back in, dope, tape, dope 2 or 3 times, and paint it. Good luck.