We are talking about the brakes here! This is what stops you. I know of no reliable way to replace the molded on end. Replace the cable they cost very little.
+
+
== Update ==
+
+
Well, if the question is "can" you. I guess the answer is yes you "can" . In an emergency, get you home situation you can tie a knot in the cable. You can even use a gear cable. Use the brakes with great care and replace with a proper cable when you get home. There are clamp on ends made for straddle cables for cantilevers and U brakes. Basically a cylinder with a hole and a set screw. Not very reliable, because the set screw squishes and damages the cable and it will eventually fail.
We are talking about the brakes here! This is what stops you. I know of no reliable way to replace the molded on end. Replace the cable they cost very little.