@jgnat, I think that's an excellent approach. Ask first and assure them that your intention or motive is not to cause them to question their faith or God. Also, making them the teacher and assuming the role of the student removes the unwarranted suspicion. The burden of proof all of a sudden falls on them as representatives of God's people.
"I can't seem to understand _____?"
"I would like to better understand your position on _____?"
"When I read this scripture I take from it _____?"
"Can you give me a little more background on ______?"
Then when they make a circular statement, press them for evidence for such a claim, "Can you prove this from: secular, ubiased, historical or objective sources to prove this truth?" When they cannot, tell them "I competely understand how you feel about this, however this seems to me like a faith claim and many people all around the earth can assert their own interpretation of the bible."
Now if you ever face the situation of interpretation and authority, knowing how to ask questions to dismantle the faithful slave doctrine is GOLD.
These types of approaches can help eliminate many of the walls associated with their indoctrination and causes their mind to start thinking and resolving the problem. In their minds, the truth has to be proven to you and can be easily answered. Keeping a classy loving attitude and tone throughout does wanders, it did for me when I read Crisis of Conscience.