How to boot KNOPPIX 4.0.2 installed on USB hard drive

Hi.
I have copied KNOPPIX DVD on my USB hard disc (i used knoppix tohd=/dev/sda1 to do it)
And now I am able boot knoppix form it by GRUB and minirt.gz (like from original DVD).
But knoppix running this way cant be updated.
Question:
Is there any possibility boot installed KNOPPIX (by knoppix-installer) as well?
What changes of initrd should be done to boot from USB hard disc?

Thanks
jpavlicek