AutoPano hands back one CR2 file after stitching several CR2 files?
So in brief, are you saying that anything pushed out by Photoshop is going to be a huge file and is unavoidable?
It depends ob what exactly you are doing, a jpg for example might even be smaller than the RAW file/s, but naturally the quality would suffer.
Did you save the tif flattened or with Layers and with which compression settings?