Sexually speaking, for the INTJ, sexuality is a caged beast. One must first get through the barriers.
But you had best be careful what you wish, because once you unleash that beast... well, I won't lie, he's gonna want a lot of sex. The more "me caveman/woman, ooga booga" the approach is, the better in my case.
Edit: I suppose that doesn't really answer your question of "how" though does it.
The key thing is, persistence. It generally takes time for an INTJ to find out if he has feelings for someone. Oh, and be direct. Game playing frustrates us. Think, "Me cavewoman, ooga booga" levels of directness.