Knoppix livecd: unionfs with another external disk

Hello everyone,

I'm looking to test some stuff with Knoppix Livecd without modifying host PC so I want to stay on livecd.
As I need extra space and I have an external extra disk, I want to unionfs it with the rest of Knoppix.
I saw there was a switch from unionfs to aufs but it seems on my system (v6.1), but there is no
mount.{aufs,unionfs}, or {aufs,unionfs}* commands.

How can I "merge" my two tree / and /mnt/changes ?

thanks a lot.
Cheers

note: I'm doing this on command-line and for now, I'm testing on 6.1 for now.