This is the broken hold cable resting on a thin wooden wedge. The copper tracks are embedded in the plastic and have to be exposed. These tracks are closer to the surface on one side than on the other. Check this carefully with a strong magnifier. Tracks will appear more clear on the near side. Place cable right side up on a thin piece of wood. Stick this down with a blob of Blu Tack and gently rub away at about 3-4mm length at the end of cable. The aim is to rub down through the plastic to expose copper track. I used one of those sandpaper boards sold for filing fingernails.

A more precise tool for this job would be a piece of fine abrasive paper glued to a popsicle stick.

When you can see two separate bits of bright copper side by side you are ready to go. Next, you need to make a cut of about 3-4mm using a sharp blade. I used a craft knife. This is not as difficult as it may appear as you can "feel" the space between the tracks if you apply a very light pressure. Hold the ribbon flat with a blob of Blu Tack and position the ends of two 3-4in lengths of 46 AWG wire as shown. I used bare copper but solderable varnished wire would be better. Hold the wires with another blob of Blu Tack and carefully nudge them into position.