there's a pretty simple way to do it actually.. take a look at any 2000 or newer suburban or tahoe backseat and you'll see something like this, sort of hard to explain but i'll try..

drill a hole about 4-7 inches below bolt for the socalled clip that the belt already feeds through and attach about 4inches of tiny bungy cord then hit up a junk yard for a little piece of plastic that the belt will feed through. place the "feeder" you get from the yard on the other end of the bungy, this pull the belt down or over a small amount. it was made for small children in many newer cars it will still be able to be pulled tight incase of accident but will be able to pull the belt away from your neck. hope that helps, ryan