I followed a thread here that used a stick of romex,
First drill a pilot hole about 3 cm deep where you think the center of your old wires are. Drill it to the size of a small piece if stripped romex.
If you are lucky you will find some new copper plug wire, 7mm. Drill a hole 2cm deep that size, stick your piece of romex in the pilot hole and then stab the new wire on. I leave mine with a bit more length than stock, and I epoxied a small boot over it, but is that really necessary? .
You can drill the large hole to almost that exact size, or as tight as you can squeeze the wire in.
Use the search feature and see what you come up with...
Edit:oops half that deep ...