it's not really a structural issue since those holes are there anyway...though your "wollered out" bit doesn't increase strength, it's probably OK as the area where that rotator bar was isn't one of the higher stress areas. I would cut a piece of a tongue applicator (or similar) and drill a hole in the middle of it. I would put epoxy on the applicator ends, put it through the hole, and pull it against the inside of the mast using the string. Let the epoxy cure. Then build up the hole using epoxy and milled fiberglass (or carbon). Fumed silica is fine - but sanding it later is a real pain. Microballoons wouldn't give enough cross linking strength to the patch.