Check out the install thread on
SIRIUS Backstage for ideas. If you can go with the PIE aux-in or 1/8" stereo adapter you will be much happier than any of the other options. I've had sat radio for a long time now and have on occasion used the FM transmitter and hated it every time. Couldn't wait until I could go aux-in again.
I've got the Starmate as well. You'll love it.