Either get canadian pillars/headliner or make a big enough slit in your pillar to pass the actual seatbelt through. Ill be doing this soon, except ill be using b12 seatbelts.
To make the hole a hot blade, dremel or maybe a soldering iron will work. Havent made my mind up on which method ill be using
check this out
http://www.240sxforums.com/forums/934056-post15.html