If you have not cut it yet, dont! there is a solution for this I use all the time. Go to your supply house or big box store and buy a 3-0 spreadder. This will have a bar on it like you see in your wall. Then get a 3-0 metal pancake box. Then take the metal bracket and two screws off the bar and use these to attach the pancake to the bar in your wall. Bring the romex wire through one of the holes and secure it with the clamp, be sure to wrap it on ground screw. Oh and make sure the power/switch is off. Good luck, hope this helps.