The great ideas from whereaminow reminded me of the base ball cap hangers I had for my boys. There were basically a long length of 8" wide fabric with strong clips about every foot which hung from the ceiling. Each hook help a baseball cap. A version to help you would be to custom locate the clips and hang a ruler from each one. You might get all your rulers hung in a 6"-8" space on one wall. The clips should be available at office supply stores.