I wish I could find the link but all I find now are instructions to use a Fedora script to create the thumb drive -- a script that doesn't seem to be immediately available for CentOS or RHEL.
I used the rpm referenced off this site if I recall right... http://fedoraproject.org/wiki/FedoraLiveCD/LiveCDHowTo http://fedoraproject.org/wiki/FedoraLiveCD/USBHowTo
jlc