I managed to open my cardale garage door, without damaging it, when the hook on the plastic handle failed leaving one of my cables hanging down.
This method will only for one of the left or right cables, and only if you haven't got 'stuff' piled up all the way to the edge of the door.
My left and right cables are about 3ft long. The plates down the edge of the door are 2ft long. Using some stiff wire, I made a hook with about a 6 inch curve. In the 1ft section below the protection plate, I was able hook the cable out of the edge of the door. I then tied some string onto the cable, and then pushed the cable and some of the string back through the edge of the door. Then I was able to get the string around the bottom corner and move along the bottom of the door until I was at the opposite bottom corner. This provided an angle where pulling on the string released the catch.
