Copy the file /usr/local/lib/knx-hinstall to home directory:

$ cp /usr/local/lib/knx-hinstall /ramdisk/home/knoppix

Open the file using your preferred editor

Look for this part:

# remove Knoppix entry from /etc/sudoers
cp -af $TM/etc/sudoers $TR/etc/sudoers

# remove Knoppix specific menu entries (they won't work without
# sudoers entry)
chroot "$TR" rm -rf /usr/share/applnk/Knoppix /usr/share/gnome/apps/Knoppix

Comment the two lines:

# remove Knoppix entry from /etc/sudoers
#cp -af $TM/etc/sudoers $TR/etc/sudoers

# remove Knoppix specific menu entries (they won't work without
# sudoers entry)
#chroot "$TR" rm -rf /usr/share/applnk/Knoppix /usr/share/gnome/apps/Knoppix

Login as root (or open the root-shell) and execute the edited knx-hdinstall:

# /ramdisk/home/knoppix/./knx-hdinstall