It was surprisingly easy...it all came together walking through the camping section at a superstore (Target/Walmart) where they sell elastic cord.
It is as easy as removing the old laces, and pulling the elastic through the eyelets. There is no need to cross them, and you don't want to pull them tight. Simply lace the elastic through and leave it so the shoe looks natural (not over tightened). I started at the bottom and and laced up to the top and simply tied a figure 8 knot in the end so that it doesn't pull back through.
It has made them almost as comfortable as house slippers that will stay on even when running!!!
ENJOY and save the heals of your shoes