How? By disabusing yourself of the notion that philosophy is other than love of wisdom. Philosophy has nothing to do with "thinking critically" (whatever that may mean to you) nor does it have anything to do with "the humanities". Philosophy is love of wisdom. It's purview is logic, rhetoric and reason, it's domains ontology and epistemology, it's toolbox analysis and it's pastime the rejection of false argument.
The translation of philosophy from the Greek has stood 2500+ years despite the term misused to mean "a way of looking at things". "Love" in the context of initial utterance was used like we now use "virtue" "respect" or "reverence". To the point, what is respected with philosophy? Wisdom. Some say wisdom is the intelligent application of knowledge, but intelligent according to whom? No. Wisdom simply obtains knowledge and that is all. What is it that is obtained? Knowledge is empirical verification of what is (else how do you know what is?) What is (i.e. the world, the case, states of affairs, et cetera) is that which is empirically verified.
Statements regarding what is (the world, the case, states of affairs, etc.) are either true or false and this has nothing whatsoever to do with perspective. Perspectival (and situational) statements are "what is true to [you; me; us; or them]". What then is truth? Truth is simply a condition of propositions (statements, assertions, etc.) which is satisfied when what is said is corresponds with what is (the case, the world, states of affairs, etc.)
Again, respect for obtaining empirical verification of what is (read: philosophy) is not a way of looking at things. If it were then an oasis and a mirage would have epistemic and ontological equivalence. They do not. If a way of looking at things were adequate for determining or even merely stating the case then the world would be flat and you could sail off it. You can not.
Ways of looking at things are to be either agreed or disagreed with like so much gossip, sentiment and opinion. Solicitations to agreement with perspectives are often offered as if they were philosophy. They are not.
For yourself and your friend, consider the instrumentalist ethos: tell any would-be philosopher that if after opening their pie hole you cannot be assured of knowing something that you did not know before, or, failing that, that you cannot at least be able to assess whether what they say can eventually lead to something you did not know before, simply tell them they have no philosophy.