Take dental floss (mine is waxed because that's what we have - it doesn't have to be), and wrap it around the spine once and tie it off on the OUTSIDE of the binder without cutting. You want it to be snug and straight - I place it in the groove of one edge, between the spine and cover. Then, neatly wrap the floss so that you have one loop (on the inside) for each magazine you want to bind. The loops do NOT need to be evenly spaced (the weight of the magazine will take care of that for you), but they should not overlap. Cut the floss.
Pull the edges of the floss, on the outside, through the loops and tie the two ends together, pulling all loops into a bundle. You may trim the ends or not, it doesn't matter.