Questions about Multisite Profiles Setup

I setup a Multisite and have a plugin that allows me to create Multisites within a Multisite Setup. The problem with this is the plugin only allows for the creation of users and profiles within each individual site. Therefore, if I create 10 sites it means that members of my main site would have to register for all 10 sites to access them and enable them to post. Is there a way I can have the plugin access the main users table in the database for user details rather than each sites individual ones? Any help would be appreciated.