I got them installed. Here's a DIY write-up with pics. The write up is just for one side -- just repeat for the other side if you put these on each side.
Step 1:
Mark where you want them mounted -- put some masking tape on the underneath side of the parcel shelf holder brackets, then hold them in place. You will need to position them so they have a place to retract into -- there is really only one spot to put them, and you want to make sure the hooks retract and touch carpet, not hard plastic to avoid rattles. I then marked an outline on the tape with a pencil, as well as marked both bolt locations).
Step 2:
Remove the parcel shelf bracket. There is a single screw, plus some hidden clips holding them in. The screw has a star-shaped head -- once you get the right bit, it was easy to unscrew. The hidden clips take a little bit of force to pull out -- start from the back (near the hatch weather strip), and pull until 1-2 sets of clips unhook (there are 3 -- rear, middle and front. Once the first 2 are out, you can reach behind to get a grip to pull the last one out. There are some pegs that help tie these into the ceiling liner piece, but that piece does not need to come out (it may start to come out -- the peg helps tie them together).
Step 3:
This step might be overkill -- but I decided to mount the bag hooks to a metal plate inside the parcel shelf bracket. I went to Lowes and bought 2 6" mending plates -- the holes were not in the right place, so I had to drill an extra hole in each one. I used a drill bit about the same size as the existing holes in the bracket (and had to drill a small pilot hole first to align the larger bit. The threaded clips that come with the bag holders fit over the metal plate, and the bolt will go through the holes in the plate before threading into the clip.
Step 4:
Prep the parcel shelf bracket for drilling. With the bracket outside the car, I made sure the marks for the holes still made sense and that both were the same distance from the edge (so the holder would be parallel with the shelf bracket when in use). Once ready, drill holes in the parcel shelf bracket -- I used a drill bit that was the same size as the holes in the bag hook. I drilled all the way through, but was careful not to hit the other side of the shelf bracket (since that is the side visible when you load thinks in the trunk).
Note -- I only marked the exact location in the car for one of the bag holders. For the other side, I transferred the hole locations to the other one (they are near mirror-image parts) -- which worked well.
Step 5:
Mount the bag holder onto the bracket -- put the bolts through the holder, then through the shelf bracket. Place one of the clips over a hole in the metal plate (thread side of the clip furthest from the bag holder), then reach inside the bracket and get the plate and clip into the bolt -- thread the bolt just a turn or two, then do the same for the other bolt. Tighten the bolts (these have a hex head...)
Step 6:
Put the bracket back in the car -- I found it was easiest to slip the back edge back under the weatherstrip, then snap the clips back into place from the front to the back (otherwise the weatherstrip gets a bit stuck behind the bracket -- it pulls out fairly easily though). Once the clips are all hooked back in, replace the one screw.
Repeat for the other side...
Here's the pics: