Yep, French aint gonna to work. The only way to do this is to fab up some steel brackets, remove the drywall and screw them onto the studs. Patch and paint the wall, slip the shelf (2 pieces of plywood nailed and glues to a cleat) onto the steel sticking out of the wall. Between the brackets there will a wooden cleat for the shelf to screw or nail onto.
We just about to finish this project with the floating shelves in the kitchen. It will hold 100 lbs easily. The shelves are sagging or point downward. its my professional photography work at best.
