Just finished putting everything back together and it works great! Basically, I put my SIRIUS antenna inside the rear spoiler. Completely hidden and excellent reception from the highest point of the vehicle. I took plenty of photos and will put a how-to page up on my web site, but here's the basics for those fairly confident with this kinda stuff:

First, you need one of the newer micro-antennas (SIRIUS or XM, doesn't matter) cause you need the guts. That's right, take it apart as all you need is the actual antenna module. Once you have that, remove the rear spoiler per the shop manual directions. Remove the the third brake light array and feed the antenna cable through the same hole as the brake wiring and stop when you've got about a foot or so left before the module would go in. Take some plastic bubble wrap (the small bubble kind) and stuff in through the hole to either the left or right side. Use a dowel or something to pack in in fairly tight as this will keep the antenna from sliding around. Wrap some Saran Wrap or similar around the antenna module to protect from moisture and then work through the hole and into the bubble wrap, then pull in the remaining cable. Leave some slack, cause now you're going to pack in a bit more bubble wrap behind the antenna module to further secure it inside the spoiler. Now reassemble everything and run the antenna cable to your receiver. I pretty much followed the stock antenna cable routing which took about 30 minutes at a leisurely pace.

That's pretty much a general guide line, you can use other materials to secure the antenna inside the spoiler. I just used what was handy and also with the idea I may have to pull everything back out.

I should have the web page up in a few days once I get all the photos edited, so if the brief above doesn't get the idea across just hang on!