Power Users can't invite external users?

In the WorkDocs documentation, in this link in the section on "Security - external invitations", it claims that Power Users can be set up to invite external users. However, in the administration panel it doesn't exist.

Our company has one administrator for WorkDocs, but could potentially have a few hundred power users. Those power users will have control over their allocated 1TB of space (and be on their own site), and they need to be able to invite external users to view a folder. Each power user might have a hundred or so external users that need to view folders in their space. What won't work at all is those power users having to contact the admin to send a link to every single external user they need to view their folders because that could potentially be 20,000+ external invitations that would be piled onto the one admin. It also won't work to make each of those power users an admin, because you'd run into the possibility that they could inadvertently create and/or invite paid users, and the cost to our company would skyrocket unnecessarily.

Bottom line, we need to be able to have power users invite external users and ONLY external users--they should have ZERO ability to create or invite paid users. Those external users need to be able to view the contents of folders that the power user sets up. Can this be done?

Thank you, -Brent