I also have a reply from McAfee that it isn't possible to upgrade a standalone Epo 4 configuration to a clustered configuration. This is because the cluster configuration is now built into the installer.
In EPO 4 the clusterconfig is an option during installation. So there will be no seperate installer.
That's also the reason why it isn't possible to change a standalone installation to a clustered instalaltion. When you run the same setup.exe it comes up with the question if you would like to remove Epo 4.