PowerCLI can be used against an ESX host directly. You don't need a vCenter server. However, if you want to clone VMs, you need the vCenter appliance. Why not just download it and be done with it?
(If you are referring to licensing issues, PowerCLI only works in read-only mode with the free editions of ESXi as far as I know.)
The Connect-VIServer cmdlet works with vCenter servers and ESX hosts directly.