Never had a problem with the way the Cruze is set up, if my wife has something large enough to fit in the trunk, I carry it out for her, hit my remote button twice, and its opened. Only time I use that trunk switch at the trunk is when the car is in the garage. For practically any other vehicle I had over the years, needed the key for this same task. Even my Supra is this way, but that I can open from the inside as well, that means going to the door first to get in, when I really want to go back to the hatch on this thing.
70 Buick had a yellow switch in the glove compartment that would open the trunk whenever you hit the button, kid hit when I was driving at 75 mph. 92 DeVille switch would only work in park and the ignition switch had to be in the run position, not very handy, but also had a key. All these cars between these years had that electric pull down motor that was more trouble than it was worth. Some idiot trying to help would slam the trunk and break that worm driven nylon gear running a rack.
And of course, you could not buy that gear, had to replace the entire mechanism for $$$$, or due to a poor electrical contact wouldn't work at all, and no way to close the dam thing. Needed to carry a rope along, but forget about locking anything in there.
At least with the Cruze can close and have the trunk locked, even with a dead battery that was another problem with these older vehicles. But no way to open it from the outside. What is dumb is putting that green release handle way at the rear. But okay if your trunk is empty.
04 Cavalier was the best, did have a trunk release button under the dash, and the seats could be dropped from the back. Cruze went stupid on this, seats drop from the inside, can break a window with an ice pick, can clean out your trunk from the inside. Even without setting off the alarm, but if it was set off, nobody would pay attention anyway, because they are always going off on their own.
Here is the circuit diagram for the LT, assuming the LS is the same.
Trunk relay on the LT is in the lower dash fuse box, up on top on the left hand side, A couple of plastic tabs can be released to pull the top forward. But don't press on those tabs too hard, will break then off.
Can't parallel contacts 4 and 5 with a switch, release solenoid is grounded through a normally closed contact. Could cut the wire off pin 2 to prevent this, but grounding the solenoid prevents a stray field from opening it, so not a good idea.
Best place to parallel a switch would be to the rear trunk switch itself. Pin 15 of BCM X8 module, other side would be ground. And this switch would be limited to working just like the trunk switch, like it won't work with the ignition switch in and in the run position.
So the only way would be to break pin 2 off the relay, and hit pin 4 of the relay with 12 volts. But if you are in the vehicle, pop open the trunk with valuables in it, someone can swipe them and run off before you good catch them.
So as far as I am concerned, just leave it the way it is, get out of the car and help that person with their goods. Either with the remote or using the trunk lid switch at the back.