You should not even have your flash (550EX) aboard your Rebel while shooting panos.
Every thing is done in manual mode. Set your dial atop the Rebel to Av. Go into your menu and set bracket exposure to +2......-2. Shoot RAW! Even though you may think it is a little extra work, it really is not (if you want quality shots).
Each stop now will yield 3 images... 12 images to go around 360. Look into Photomatix for your three shots at normal exposure, under and over. Merge the images and you now have an image without blown windows
I am sure this topic can be found over and over using the search.
Good luck to ya,