Yep!
It's called ripping.
You can remove the update files out of it. That usually takes out ~20-27 megabytes depending on when the game came out. Sometimes too, you can delete movies (.PMF) and music.
After that, you can compress it into a .CSO file using a compressor. I don't have a link but you can Google for one.
Usually that can take a good 40% off of the filesize.