Wait a second! You've tried burning Knoppix as the first session of a mutli-session CD, and were able to add more files as a second session, and have the CD still boot? How did you manage this on a CD?
Sorry, my mistake. I meant that I used a version of Knoppix I'd trimmed down to 500Mb or so (removed lots of ancillary software and added about 20 Perl modules for my development environment), and then added more via multisession.