The headliner does not need to be removed. They do recommend a 'bit stop' so you won't drill through the headliner, but if you're careful......

 

Folks

I have succesfully carried canoes, roof bags, ladders etc on my HHR with no rails.

If you open the doors you realize how much is between the doors and chassis, so I hook a strap to the door hinge run it up the colum. The doors close properly, nothing gets caught or pinched.
For the rear i run straps under the hatch and hook to the loops on each side of the floor.(not the ones on the sides they are plastic)

Am sure if someone woudl spend the time it would be easy enough to come up with a complete rack using this method to attach.

am working on my own right now using oak side rails and pipe flanges and 1/2pipe, will post pics when complete