CentOS 5->6 Upgrade [duplicate]

CentOS 5->6 Upgrade [duplicate]

This question already has an answer here:
Why is it so difficult to upgrade between major versions of Red Hat and
CentOS? 2 answers
Has anyone managed to upgrade centos 5 to 6 without doing a full reinstall
from CD? (I.e. using yum) . I know its not "supported", but I have to
upgrade hundreds of boxes accross the globe, with no physical access, and
no iLO.
I think i should be able to upgrade a few prerequisites like rpm, yum ,
and upgrade centos-release then yum update, and use yum-utils to clenup
any obsolete packages? Is that equivalent to "linux upgradeany" ?
Has anyone got a story to tell about it?