Hopefully this doesn't seem too insensitive, but think about this from another angle: Why should he start conversations? What incentives exist for him to start talking to you? I mean this as a sincere and serious question as you may believe there is some form of emotional payback that comes from interactions but this may or may not be the case.
As for general ideas, keep in mind the feedback you give can go a long way towards whether or not you get a lot out of someone. For example, if I knew that I'd get a smile or good laugh out of someone for saying a handful of words this may help as information to nudge me towards trying to open up. Just be aware of what feedback you send as there is usually something being sent, whether verbally or non-verbally. Sticking to one's interests can help though don't forget that the INTJ may wonder, "Why would you ask me that?" which can lead to various paranoid thoughts of course, but this may or may not be what you'd want to see.