You can also try this: Ask them what religion they belonged to before becoming a JW. There's a good chance that one of them was a Catholic. When they say they were Catholic you just say: "So that means you're an apostate and I have no dealings with apostates!" then you close the door and leave.
Alternatively, you can take the same platitudes and rationalizations that JWs use to excuse Watchtower's errors and injustices (imperfect men taking the lead, the light gets brighter, that was in the past, wait on Jehovah (or "the LORD"), etc) and apply them to your own church to justify remaining in your own church despite its errors. Just change the wording slightly to avoid suspicion that you're mocking them. Give them a taste of their own medicine.
Another thing you can do is ask them for advise on how you can help your friend escape the clutches of some obscure cult. Just make up a name for the cult - preferably a name that is not the name of an existing cult, so that the JW will find nothing online if they researched it. (It's a very obscure cult) Then you describe the cult to them making sure to mention characteristics that are very similar to JWs. For example you can say that the cult:
~ Teaches that they are the restored true church and only they are true chritians and it labels all other professed chrisitians as being part of "churchianity".
~ Teaches that the cult's leadership council was divinely appointed by Jesus in the year 1939 to teach true christianity. They are the only channel of instruction that God is using today. Members must trust the leaders and accept their teachings to have God's approval. Persons must serve God in association with their group to have any valid hope of surviving the end of the world.
~ Forbids invasive gynecological exams citing the command to "abstain from fornication" mentioned at Acts 15:28,29. As a result female members refuse to get pap smears and male members refuse digital (with the finger) prostate exams. The result is that the death rate from cervical cancer and prostate cancer is higher than average, among members.
~ Teaches members to not have friendship or close association with non-members because they will corrupt them spiritually.
~ Shuns those who resign from the cult - including their own family. Shunning causes some to commit suicide because they find themselves all alone since they never cultivated friendships with people outside the group.
~ Teaches that the end of the world is coming soon and only members of the cult will survive. Because of this the cult discourages university education and many members forego getting a good education and end up struggling financially later in life.