You could leverage the profile parameters that can be set on the Adobe Target call (profile.*). Any parameters that are sent will eventually show up in the Audience builder. Not sure if you are using tntId or mboxthirdpartyid as the unique identifier.
Thank you for your reply. Not really.... the audience has already been created. My questions is more about the correct set up when adding this audience to target. The idea behind is to identify on page load, and deliver custom code if they are on a specific audience.