Internal Candidate Pool based on employee Job

Summary:

We would like to invite internal candidates who are in a specific JOB (on assignment) to apply for a requisition which will not be posted on teh internal career site, we will set the option 'allow candidates to apply when not posted' on the requisition.

We would like to create a candidate pool for these employees and then either add them as prospects to the requisition, and invite them to apply, or we can run a campaign referencing the candidate pool.

Looking at the candidate pool options and the campaign audience options, I do not see a way to specify the exact Job to get the required candidates.