How can I create protected content limited to active prosite members?

I have a multisite with ProSites. On one of my sites that I use for general information and sign-up, I would like to add some private content that would only be available to active Pro Site subscribers.

I have the plugin Join My Multisite which would make them users on this particular site but this approach would not be limiting to active prosite subscribers.

Do you know if this is possible? Or do you have any other suggestions for providing exclusive content to the prosite members?