You know I thought about you yesterday when I was at Pep Boys getting the bulbs for the foglight mod. I always browse the "rice and taco" aisle for comic relief and saw the bits and pieces to build your own "modular" air intake. Heres a link to the site:
I'm sure you've seen these given your comment about how much you've searched. Something to watch out for though - while I had my car taken apart to install the new bulbs in the fogs, I pulled the airbox to see if I could run some sort of duct as well. Theres plenty of room to run it right up until you reach the box itself. At least with the normal CTS bumper, there doesnt appear to be enough clearance to get a 3" or so tube to where I've made my hole. I did get some good ideas for a purely custom cold-air intake route that would start between the grill and radiator, then travel around and to the motor, but this would require the removal of the entire stock air intake and I'd have to use the filters sold by that site I listed above. Having already dropping $40 on the Airhog, it is hard for me to justify this sort of endevor right now, plus I dont want to have to mess with whatever sensors and such are along that route.