This should be able to be done via a mapping component... assuming there are a collection of POs per job, you can use a PO ProcessTypeMapping to create a mini-flow to manually associate the correct POs with each job.
The ProcessTypeMapping for the POs would look like Start-> (use a comp to look up POs by the job number -> End (where reults are the result of the query).
You could try doing the entire job collection mapping with a Multi Value Mapping component (this resembles a Single Value Mapping component, but is used to process entire collections vs single values)