The mounting brackets they came with allow easy pivoting/aiming of the lights up or down. For left to right aiming, see the explanation below.
The area where I mounted my lights is curved as well. The easiest location to mount them would have been to mount these in the center section of the lower fascia or the sections just under the bottom corners of the license plate. But I didn't like the look when i mounted them there, which is why I mounted them on the outside sections...Because of the curve, I couldn't install the mounting hardward directly onto the plastic of the bumper cover/lower facia (all one big piece). Instead, I:
1) Took a strip of aluminum about one inch wide and five inches long and cut holes to fit the mounting bolts for the mounting brackets for the lights.
2) I then positioned the lights straight ahead, sitting on the top inner edge of the plastic fascia/grille opening (where you see the lights in the photo).
3) With the lights positioned where I wanted them, I took the aluminum and placed it onto the screws for the lights and tighted the mounting bolts so that on top was the mounting bracket (with the light) and in the middle was the plastic of the bumper/fascia and then underneath was the aluminum strip. Tighting the mounting screws basically clamped the lights to the bumper. The bolts don't go through the plastic of the fascia. The shaft of the bolts actually rest against the back edge of the fascia.
It's basically like a big alligator clip, but instead of a spring holding the clip closed, two bolts with nuts hold it closed real tight.
I just loosened the bolts/nuts a little to aim the lights from side to side.
If you push on the lights back hard enough, you might be able to push them off the lower lip that they are mounted on since they aren't physically screwed into the plastic, just clamped on. But I've tried pushing pretty hard without moving them and they've been on a the car for about two weeks and 1000 miles without a problem. Heat hasn't been a problem either. I haven't decided whether or not to remove them and add double-sided tape though. I'm satisfied with the horizontal aiming right now, just need to aim them away from the ground a little.
Sorry this explanation is so freaking convoluted...