I've been building them like normal. They aren't exactly 0 rebound, but it's a very small amount. I fill the body of the shock up with oil, pump the air bubbles out like normal. Then I extend the shock, then plop the bladder on the top, seating it by pressing the top edges of the bladder down gently. I leave the foam out of the shock cap, and I actually drill a very small hole in the plastic portion of the shock cap to release any trapped air above the shock bladder.
This produces a fairly "dead" shock. Very little, and slow rebound. This really only works well on smoother tracks, so if your track is bumpy just build it the same, but don't drill holes in the shock cap, and run the foam inserts.
-Korey