How to activate a private theme for just one site in the network using Pro Sites?

I have a question about Pro Sites.

As a Super Admin, I can activate any plugins for any sites in the network, even if the site owners are not in the level that the plugins are assigned to. However, I don't seem to be able to do the same for themes. So, I am wondering if I missed something? Or this feature was never implemented?

Any help would be appreciated.