Add/update a license key with powercli script - standalone host

Does anyone know how to add/update a license key with powercli script.

I can do it OK with LicenseAssignmentManager when connected to vcenter server, but i can't do it  when assigning a free license key to a standalone host as the ServiceInstance.Content.LicenseManager.LicenseAssignmentManager is $null.   (esx5-623860)

Cheers,

Matt.