Has anyone used a cargo topper/roof topper on their HHR without a luggage rack?

I have a new topper that I purchased for my Navigator that I hate to get rid of but it doesn't seem like I will have any way to affix it to the top of the car without a luggage rack.

Any thoughts or info is appreciated.

 

Boy I'm struggling to see a way to do it with the doors being cut into the roof rails on the HHR, nowhere really to attach the cargo topper. I'd almost think in order to use it properly, you'll need the roof rack just as an attachment point.