Adding a backing of 1/8" will likely double or triple the drawweight. It could as well overpower the belly ERC laminate. It depends on how much you want to increase the drawweight, but I don't like the idea of adding a second backing onto an otherwise decent bow. Shortening the bow might be better if you want only a few extra pounds. Removing the current backing and replacing it by a new backing that is 1/16" thicker might be better if you want to increase the drawweight by 10-20 pounds or so.
But you might just consider starting another bow and call this one underweight...