Wow, that's a tough one... Is it broke at the hood latch, or inside? I had one break inside on another car, I had to use pliers pull the cable to open the hood.
If at the hood latch? Man, that is going to be tough. Look up through the grill and locate the hood locking mechanism. It will be in the middle of the car, directly under the front of the hood, of course. Bend the end of an aluminum wire (or like a wire hangar) around to create a loop, then tie a knot so that the loop does not come loose. Slide the wire through the grill and get the loop around the hook of the hood locking mechanism. Pull the wire in the opposite direction of the hook while depressing the hood. This will give the hook some slack and make it easier to pull open.
There are other ways, but some are car and model specific.
There is no way to jack it up, and reach up there and pull it manually, because there is no room to get our arm up there. You have to do it from the front.
Some have done this with Cherokees, or removed the headlights to get to the latch mechanism.
One liberty owner said: "If you can see where the cable connects to the release arm you can force the arm over with a screwdriver and release it ."