Unbeknownst to some of us, Klaus K included a useful new command-line
feature in Version 7.4 Knoppixes.

This is to provide an example of a new capability in Knoppix 7.4 to create
a LiveUSB directly from a downloaded Knoppix LiveCD- or LiveDVD- iso,
without first actually making a LiveCD or LiveDVD for that iso.

Using a Knoppix 7.4 LiveCD, LiveDVD or LiveUSB command line
flash-knoppix KNOPPIX_V7.4.2DVD-2014-09-28-EN.iso
brings up a usage chart which will allow creating a 7.4.2 LiveUSB directly
from this iso definition, which if correct and found, doesn't itself need repeating.
The usage chart looks like this:
Usage: /usr/bin/flash-knoppix [-a] [-f] [-m i|p|n] [-p mb] [image|dir] [target_device]
       -a            Allow fixed disks
       -f            Force overwrite, no questions (batch mode)
       -m i          Method: Create overlay image
       -m p          Method: Create overlay partition (recommended)
       -m n          Method: No overlay (read only)
       -p mb         Overlay partition or image size in MB >= 200
       image.iso     Loopmount source ISO file
       dir           Source data directory containing files
       target_device Destination block device (flash disk)
For my 16 Gb SanDisk at /dev/sdc and my iso at /media/sda3/isos, and
assuming 5 Gb for reiserfs persistence, the usage which worked was:
/usr/bin/flash-knoppix -m p -p 5000 /media/sda3/isos /dev/sdc
FWIW, I download & keep my isos on a Win7 ntfs partition.