I agree with Drew, as well. I don't think they will be mentally up to a multiple point discussion and will fairly quickly get the hint they are going to badgered into leaving, a feeling few JWs will tolerate for more than a minute.
I understand that your friend thinks Bible study aids are (or should be) unnecessary. But he will never become a JW without changing that opinion. I think there is enough to hang them in their own primary study aids that there would be no need to step outside their comfort zone.
Sun Tsu would argue that removing the supports of an enemy with seeming ease, in an environment where he feels himself most safe, will shake his confidence more than anything else could.
This line of thinking is in favor of using their primary study publications and sticking to a single issue, or maybe only two issues. After all, you aren't introducing the publication to teach the Bible from it. You are introducing it to challenge their teachings, as to whether or not the teaching have Scriptural basis.