I use something called "Waschbenzin" to clean jewel cases and also discs. Removes grease and also glue residue. I know the fog effect from using ethanol or acetone e.g., where the latter heavily reacts with most kinds of plastic. Waschbenzin is much milder, and I haven't yet noticed any effect on the transparency of the plastic
I'm not sure how to properly translate Waschbenzin, but here's the
Wikipedia entry.
And here's an image of the back side of the can, shows the ingredients: