AS Obfuscation

I have been searching for a program that will obfuscate my class files and not just the SWF, so that when I give the source files to the client they can change/view the flash AS but not the class files that were built for them. Basically I have various tween, layout and XML classes that I would like to keep proprietary because I worked really hard to make them. Has anyone heard of anything that can do this? Thanks :beer: