My previous two cars—Scion xA and Chevy Sonic—both had spoilers. I thought this was going to be a huge problem, but in the end I found that using the right rug to protect the spoiler was the simplest solution. The best mat I’ve ever found is a closed-cell rubber mat (not foam) about 3/8" thick that is sometimes used to relieve foot pain (“anti-fatigue” mat?) These are cheap and they don’t compress over time. They stick to the car roof well, yet the kayak slides over them pretty well. They’re heavy and sticky enough that they don’t blow off in the wind. They protect the car better than the commonly recommended rubber-backed bathroom rugs.
The question is—and I think this is your main worry—will the weight of the kayak bend the spoiler? On my two cars, there was no damage to the spoiler. My kayak weighs 45 lbs, but the spoiler doesn’t really bear the full weight of the kayak, or for very long, if you load it right.
Rather, the spoiler becomes a brief pivot point just long enough to tip the kayak up onto the rack. (I use Thule saddles, not J racks.) Procedure:
(1) If material is other than rotomolded, place a 6’ rubber mat about 6’ behind the car (or father back for a longer kayak like yours) to protect the stern
(2) Set the bow as close as possible to the rear of the car.
(3) Pick up the kayak by the coaming, pull it forward (making sure the keel is on the rug), and lean it lightly against the spoiler.
(4) Bring the keel a bit closer to get the kayak as vertical as possible.
(5) Lift the keel and push the kayak onto the rack. If you’ve placed the kayak as vertical as possible, you’re not really pushing it against the spoiler. You’re just tipping it up onto the rack.
With a shorter kayak (mine is 13’5") you can also place the kayak on the ground parallel to the rear of the car, lift it by the coaming, and tilt it up so the bow clears the right rear corner of the car.
The KIa Nero has a bit of an odd shape in the rear—the spoiler looks to be set fairly far forward while the rear of the car protrudes outward. That is, your rear is pointed rather than square. A spoiler on a square back is easier to deal with. You will want to make sure that the rubber mat is long enough to cover about 16" of the car roof, the spoiler, and the rear window.
My main point is that spoilers aren’t always as fragile a you might think, and the contact between the kayak and the spoiler could be lighter and briefer than you imagine. I even carried my bike on a rack by protecting the spoiler.
I tried other solutions—a Malone rear loader, Thule roller loader, and homemade contraptions. In the end the closed-cell rubber pad protected the car the best and was the simplest and cheapest device.
Caveat: If you carry a bike, kayak, camping gear, etc. on your car very often, eventually you’re going to have dents, scratches, and worn paint no matter how careful you are. This is the price of carrying stuff on your car.