It should work, if you first boot with cheatcode "Knoppix 2" to boot as root so you can install RealPlayer 10 to directory /mnt/sda1/RealPlayer10. Sudo su when needed should do the same, though, but is less convenient. Place a script in on the same drive like this for RP10 -

#!/bin/bash

ln -s /mnt/sda1/RealPlayer10/realplay /UNIONFS/usr/bin/realplay
ln -s /mnt/sda1/RealPlayer10/realplay /ramdisk/home/knoppix/Desktop/RealPlayer10
ln -s /mnt/sda1/RealPlayer10/mozilla/nphelix.so /UNIONFS/usr/lib/mozilla-firefox/plugins/nphelix.so
ln -s /mnt/sda1/RealPlayer10/mozilla/nphelix.xpt /UNIONFS/usr/lib/mozilla-firefox/components/nphelix.xpt

When you reboot as user, do at a terminal:

$sudo su
#mount /mnt/sda1
#cd /mnt/sda1
#./ScriptName

and the executable script will activate the final gui portion of the RealPlayer10 install as well as symlink the Firefox plugins for the embedded audio/video stuff, which has worked well for me with Firefox.