I vote for going ultra-hardline, but back everything up with references to the WT. If you give a talk that your conscience is OK with, then you would only be serving to soften the face of the cult to anyone there who assumes you're a JW (i.e. everyone). You never know who in the audience might have a problem with something in the cult (in this case, perhaps the call for obedience even if it doesn't make sense) and if you soften the blow you might serve to keep them in the cult longer.
That or spin things such that you're directly condemning the cult in some way without saying it. My favorite talk ever was the one about 8 months ago where I got up there and talked about how we would never want to be a part of any religious organization that had ties to the UN. It was hilarious and sad at the same time to see all the nodding heads.
Anyway, you're never going to reform the cult. Certainly not by giving softened talks that could pass for legitimate christian sermons. I think the only way to help is for anyone who's still in to point out the flaws by making them obvious, either by citing inconvenient scripture or by going ultra-hardline. A talk about obedience seems like a great time to do the latter.