Using the vSphere API to Register a vSphere Client Plugin with VCenter 5.1 server

Hello

I am attempting to use the vsphere API to register a vSphere client plugin. I am programmatically creating an Extension object and filling in the extension details. However I am unable to set the client and server information. Looks like the setServer and setClient methods are not available for Extension object. Is it because it is not supported on VCenter 5.1? If yes, what is an alternative?

My end goal is to write a tool that will deploy my plugin package onto the VCenter server so it can be available to all vsphere web clients, connected to that server.

Any help is appreciated...

Thanks

Elizabeth