I think you can open your rear trunk by removing the left rear bumper and fishing out the secondary opening cable. The cable exits the trunk just under the left tail light. Here are some pictures.
inside the left side of the trunk - cable exit
About where it is from the outside of the trunk
So it looks like you could take off the left bumper off, and fish for the manual cable with some 12 gauge copper wire and pop the trunk. I could not see the cable using a flashlight with the left bumper off.
Threaded Mode
