this is already possible.
Knoppix itself is just a single 695MB file.
Add any multimedia data you want, then create a new ISO.
specify the same boot image as that was originally used.

here's my 3GB disk. Knoppix directory still contains everything, unmodified.

S:\BootCD>dir /b
AUTORUN.INF
cdromsp4.tst
CDROM_IP.5
CDROM_NT.5
snapshot.exe
WIN51IP
win51ip.SP1
w2k4
Programs
KNOPPIX
isolinux
i386
FREEDOS
data
LOADER
REACTOS