Here's a link to dinghy information:
http://www.motorhome.com/download-dinghy-guides/. Go down the list to the 2011 Dinghy Guide.
According to the 2011 dinghy guide, Chev HHR (both manual & auto) can be flat towed. Note in guide says to remove Fuse 8 from floor console fuse block while towing. GMac's comment above pretty much covers what you'll need.
Be sure to check the HHR's owners' manual as well for any additional info about flat towing.