When I would make as obvious reductio ad absurdum like "Well if you asked 100 people if the world was flat in 1066 ..." he would say things like "I don't like your analogies..." as though my example had nothing whatsoever to do with what he said. Ayn Rand helped me realise he was "concrete-bound" he didn't know how to move from a specific example such as "if you ask 100 people they will disagree with you (on this issue)" to the underlying principle of the assertion (the truth is what the majority says it is.) Have you any experiences of interacting with the "concrete-bound" ?
I have found a method of intervening in a way that helps explain the leap but it requires a bit more patience.
You have to first make explicit the principle, "are you saying that if most people believe something then that something is true?" - Wait for them to respond. They are unlikely to say yes, if they say "no - but..." listen to what they have to say and then respond, "But you accept that just because the majority of people say something is true that doesn't mean it is true?" and proceed in the same fashion without hostility so avoid provoking defensiveness.
In other words: don't skip steps in your reasoning, and don't use hidden premises. Take people through the argument stage by stage.
Afterwards you can explain the concept of the particular logical fallacy