shock cord makes jack purcell much easier. this is MSR's silicone-core product intended for replacing tent-pole cords. you will also require scissors (make sure the blades are sharp) and an open flame (a lighter or gas burner will work).
do not pre-cut your cord. choose a hole to start with (A; above, the toe-ward outside hole) and thread from the outside in. the loose end of the shock cord will end up protruding from the last hole (B; above, the heel-ward inside hole) while the spool end will protrude from A. pull through to leave about 2-3 inches extra on the B-end. coarse adjust for tightness (err on the side of being a little loose), then cut the A-end of the shock cord and tie a stopper knot in it. adjust for tightness again and tie a loose stopper knot in the B-end. repeat on the other shoe. walk around for a bit to be sure of things. try the shoes with socks and without. when you're happy with the fit, secure the knot and trim both loose ends to just shy of the stopper knots. wet fingers and seal the cut cord ends quickly with an open flame, pinching immediately with wet fingers to fuse the melted sheathing.
walk around smugly.