I am able to make a Centos 5.x AMI by following steps similar to those outlined here:
http://docs.amazonwebservices.com/AWSEC2/latest/UserGuide/creating-loopback-s3-linux.html
and detailed here:
However this process does not work as noted for CentOS 6 because there is no Xen kernel. Is it possible to create a CentOS 6 AMI either using an Amazon-provided kernel or some other kernel?