Instead of just upgrading the whole distro how about simply checking out the packages/software you want to upgrade and install them separately through RPM's. If your server is still functioning fine then you may want to leave it that way instead of risking making changes.
To be honest, RPM's are not as good at dependency fixing as Debian packages so I wouldn't be too hopefull if you did find a way to upgrade automatically - a re-install is probably less time consuming at the end of the day.
One glimmer of hope is a tool called apt-rpm which can be found at http://apt-rpm.tuxfamily.org/.
I haven't tested it out but is was recommended in a similar situation to yours by LXF magazine.