stevey_frac -
I agree with ChrstphrR, MetroMPG has a really good DIY.
If you don't want to drill any holes, then you need to figure out how to "reuse" whatever existing holes you have. I found some (partial) pictures of Cobalt fender liners :
http://www.griptuning.com/ImgApp/install/0000000130.pdf
(Look on page 10)
From these pictures, it looks like there are a lot of fastening holes to work with, at least towards the bottom.
Can you remove your rear fender liner and take pictures, or count the number and location of fastening holes you have?
Even if you don't use the existing holes, you can make holes in the inner fender liner as needed. This is a *replaceable* piece of the car that doesn't serve an aesthetic purpose. You can always restore the car by covering the holes or getting another set of fender liners.
CarloSW2