reference an entity outside of the node/add or node/edit forms
You could use the Views and Rules Link modules (along with the Rules module) to accomplish this.

What you would do is create a Rules Link that will attach your line item (exam) to a Job (that the user selects).

You would likely need to have an  field available for Rules to manipulate, but there would be no forms involved directly using an Entity Reference field (no forms involved).