Warm the ski to room temp and clean the wound with a knife to remove any rocks or shredded P-tex. Cut away the material around the gash that isn't stuck to the base, angling your knife to create a 45-degree bevel.
You'll need a flat-tip, electrical soldering iron. You can buy one for around $30. You'll also need P-tex wire, which costs about $4 for a four-foot roll. If the core shot is next to an edge, you'll want to use Wintersteiger's Metal Grip, which will better adhere to the metal edges.