Zaino ap[parently is a good glass polish for this. How effective, I cant comment. Failing that it would be felt pads, DA polisher and cerium oxide. Not for the faint hearted nor unskilled imo that option.
I have some scratches on my wifes 120D and I have tried by hand to get them out. I need to try my megs G220 polisher to try and get them out a bit more.
Zaino is what I use with good results, applied with my porter cable on a specialty pad. As long as you're not expecting the same kind of results as you can get on paint work, cause' that just won't happen.