VMWare upgrade.

Hello,

My vCenter 5.5 connects to a few hosts.  I am in the middle of upgrade the version from 5.5 to 6.

I setup a new vm and install vCenter 6 and also setup update manager.  I have removed a host (in maintenance mode) from the current vCenter 5.5 and add it to vCenter 6 and upgraded the host to version 6 using update manager.  

I am ready to remove the next host from my vCenter 5.5.  However, this host has a couple of important VMs in it.  Without putting it in maintenance mode or shutting down any VM, is there a way to add this next host to be upgraded into the vCenter 6 so I can perform the upgrade?

Please advise.  

Thanks.