There's a copy of the OEM rail installation instructions here, scroll down a bit.

For anyone struggling with the limitation of the factory rails or aftermarket cross bars, consider having permanent track installed. If done professionally you don't have to worry about damage or leaks.

The system consists of two low profile, aluminum T-tracks (both Thule and Yakima make a version) permanently attached to the roof with self expanding anchors and bolts (no need to drop the headliner). Very tight connection, can be made absolutely corrosion and leak proof, typically guaranteed for the life of the vehicle. Once the tracks are in, you can use Thule or Yakima bases that lock into the tracks and accept various towers. Gives you the ability to have a much wider spread, and are actually stronger than the OEM rails, since they are attached at more points. Plus, you can remove the entire rack apparatus in seconds and leave only the very stock looking and low key tracks, which generate no wind noise and do not effect MPG.

In my case, I realized there was no way to get bars level with the factory rails, fixed point towers, or clip on towers. For the stuff I carry, I need a solution that wouldn't point my cargo skyward, where it can catch air that generates lift. With the track system, I can move the forward bars far enough toward the windshield to drop it level with the rear bars (it's about a 40" spread, so that's a much more stable base as well).

I realize that many people are going to flatly reject drilling into the roof of their new car, and it took me a while to come around. But once I realized that there was not going to be any other way to make a rack on this car work for me, and once I talk to the installer enough to be convinced that they could do the work (and had done the work many times) without any compromise to my car's integrity, it started looking like a great solution. Way, way more flexible than any other rig.

Here's what the track looks like (not my car)