[CentOS] The easiest way for Fedora 14 to Centos 6 migration?

I manage several Fedora 14 servers. They was not upgraded due to
several reasons (systemd unreliability, K12LTSP support absence),
some newer packages I was building & updating manually, some
other (OpenOffice, Mozilla) was possible update from projects
binaries.
Now I consider the options to migrate them to Centos 6, possibly
the easiest possible way. What I'd like is some as yum configuration
files replacement of those from Fedora with files from Centos - and
then simply do "yum update".
Has anyone tried to do a similar migration? What procedure would you
recommend?

TIA, Franta Hanzlik