loosen it, close it with a friend inside, hold it where you want, have him tighten from inside............
Also, provide him with a screwdriver & flashlight, then show him how to unlock the trunk from the inside (slot in the back of the mechanism). This will put his mind at ease...knowing that he can get himself out if need be.
Fitting the trunk lid for a tight seal is very important. I had to adjust mine twice after putting the car back together, as I was getting exhaust fumes pulled in through the trunk lid seal.
So this is really the way to do this? I mean it makes sense, but it does feel like I'm being punk'd a bit.......