Directory and Classifieds with Multisite

Hello All,

I am trying to build a MultiSite community. My goal is that I am running one multisite, that the users will sign up to host their sites. I would like to include a directory page that the user and nonusers can add their business listing to and also a "global" classified page that all users can post their items for sale.

My problem is - how can I add the Classified and Directory Plugins to only my main site. I do not want the users to be able to create their own classified or directory pages. Upon installing the plugins, I see that I have to Network enable them in order to use them. The only solution that I can think of is to either pay for separate hosting for these pages, or to install WP in a subdirectory of my current domain for each of the modules.

Any help would be greatly appreciated!