You might argue that your student, while safe in the air, doesn't overtly demonstrate these qualities during normal conversation, since it's not a part of his personality. My advice for that student is to do what he or she often does on a first date--act like the person you think the other individual wants you to be. I'm assuming that a student won't be disingenuous when acting out these qualities. Instead, he or she will simply exaggerate them for easier detection. The examiner isn't just asking, "Does this person have a collection of mechanical skills?" He's really asking, "Is this person ready to be a safe pilot in command?"
So the next time you're preparing a student for a practical test, give the person some feedback on his or her demeanor. Let students know how they're coming across to you--and how an examiner might interpret their behavior. Help them to convey the persona of safety, confidence, and humility that all examiners want to see on a checkride.