I am not a legal expert, but if I were you, I would put my proprietary software on an USB stick so that it is completely separate from the Knoppix CD. This way, it would be obvious for everyone which part is Open Source (the CD) and which part is not (the stick).

If you have to combine everything on one CD, you should do as much as you can to not make it look like your software was "part of" or "integrated with" the rest. Remember, most law professionals are not IT professionals