Perhaps this line of questioning could agitate a JW's thinking. It can't hurt.
YOU: Is shunning a Biblical teaching?
JW: Yes.
YOU: So it must be God's law?
JW: Yes.
YOU: If it's God's law, can it be disregarded by some JW's, but not others?
JW: No, of course not, all Christians must obey God's laws.
YOU: So God's laws don't depend on where a person lives?
JW: Huh????????
YOU: Well, according to your religion, if a JW who lives at home with their parents and siblings gets disfellowshipped, their family association continues as normal. But if that individual later moved into an apartment next door, they would be regarded as if they were dead. Can you show me in the Bible where this discriminatory "law of God" is laid out?