If that doesn't work, there is also a wire pull that releases the rear trunk. You can see it in this picture I took when we installed my Dansk muffler, and pulled the rear bumper off the car. The wire is located right below the left tail light and you can see it going thru a hole. Unfortunately, to gain access to it, you'll have to pull off the rear bumper of the car (instructions below). Maybe if you're lucky, you can just remove the rear wheel well liner, and see if you can fish out the wire to yank it, but probably not likely.
To remove your rear bumper, first remove the bumperettes (the two rear bumper guards) by removing them with an allen key in the hole below each bumperette. Then, remove all the screws underneath the bottom side of the bumper. I think there are 6 in total along the bottom, plus one on each side located inside each rear wheel well. The final screws holding the bumper cover on are located on top of the bumper cover, but those can only be accessed by removing the rear spoiler.
To do this, just manually raise the rear spoiler (turn your ignition on, and press the rocker switch that is located near the fuse panel in your footwell), push out the plastic pop rivets located in the black metal portion of the spoiler (you'll be able to retreive and reuse these once you remove the spoiler frame, as they drop into the frame), and pop off the painted top portion of the spoiler. After removing the painted top portion of the spoiler, you will be able to look down the hollow black metal frame of the spoiler and see two hex bolts. Remove these, and you'll be able to pull out the metal frame, which then gives you access to the screws holding the top of the bumper cover. Once this is done, the bumper cover is free, but remember to disconnect the electrical wire that connects to the license plate bulbs before fully pulling out the bumper cover.
Tip: When putting spoiler back on, tighten the hex bolts that secure the black metal frame of the spoiler while the spoiler is in the fully retracted position. If you secure the bolts with the spoiler up, when you retract the spoiler, it will end up sitting a bit too high from the bumper, and it will look like there's a gap between the spoiler and the bumper when the spoiler is in the down position. Good luck.