Sounds like you dealer sucks. I had the same issue with my dealership. They had the parts but no instructions. They were gonna wing it and charge me a few hours labor to do it. I just took the parts home and did it myself. The link below will get you the XM install instructions. Its the same for the Sirius for the pages I mentioned below. The XM reciever gets mounted in the rear of the car! The thing thats freaking out the dealers is that the Sirius kit comes with a wire harness that is only about 3 feet long. So obviously its not going to reach the rear. I just tucked the reciever behind the Passanger side kick panel. It took me less that 30 minutes to do the entire install and shared the info with my dealer. I'm sure that whenever toyota gets around to providing the install instructions I'll go back in and do it according to factory spec. But in the meann time, its fine and works perfectly.
http://brockandbecca.com/files/fj/Radio/XM%20Radio.pdf
Pages 8 - 15 are all you'll need. You dont need to remove anything to install the antenna. Even these instructions are too involved, I just tucked it behind the rubber seal in the passanger doorway down to the top of the Kick panel and right into the back of the sirius reciever.