Using Editor's "joined" attributes as part of the filters on the DataTables object

Hello,

I have the following JSON object from an Editor's join:

DT_RowId:  "row_1"
customer: "10"
release_id: "4"
project_name: "Project 1"
project_manager: Object { id="6", name="First, Last"}

In my screen, I'd have two select buttons used to filter by "release_id" ('projects' table) and by "users.id" (join attribute, based on project's id and manager's id (located in 'project_pm' joining table)
The first filter is plainly applied, being the 'release_id' a 'native' attribute in the DataTables object, e.g.: dtObj.fnFilter(release_id, 0, true);

How do I 'set' the users.id as part of the DataTables attributes to be able to apply filters on it as well? Or,
How can I use dtObj.fnFilter to reach down to project_manager.id attribute?

Hope I'm making my self clear, if required I can share the associated files.
Thanks in advance