Talking about leisure-related things can get through where an out-and-out attack on LRH will do nothing but send them scurrying back into the clutches of the cult. No 'drill' or 'tech' is required... just talk about how you enjoyed the sunshine at the weekend, working in the garden. How your grandchildren are learning new things all the time... maybe recommend a favourite recipe and offer them a chance to come and try it.
None of this is particularly confrontational, or at least it needn't cause a conflict between you and the person you're hoping to get through to. What you're doing is giving them a glimpse of life on the outside: people caught up in Scientology servitude never have enough time to cook really good food or to see their loved ones; and they never have enough money either.
Every time you natter about a book you just read, or a concert you went to, etc., you're subtly reminding them of all the things they have given up, in favour of endless recruitment, fundraising and so on. You're showing them that the 'trouble source' in their life is Scientology.
Sooner or later, the only other thing you'll need to do is let them know that you have a spare room where they can stay for a week or two, until they make new plans, and begin a new life as an 'ex'.