Stool seat: Weave together the straps across the top of the frame, pull taut, and buckle each one underneath (if any of the belts are too long to stay tight, use an awl or utility knife to make extra holes). Trim off any excess leather, and take a load off.
Box pulls/handles: Using an X-acto knife, cut two vertical slits through the front of each box (as tall as the belt is wide), thread the cinchers through, and fasten in the front. Glue the rest of the belt around the inside edges of the box so it won't interfere with the precious cargo within.
Simple and to the point, although we're not in love with the idea of an obvious belt hanging on the wall. Maybe try a variation of this idea: cut off the buckle altogether.
The site only describes one treatment, making Modular Drapes, so we're guessing the other three must only be available in the magazine's hard copy.