some seat belt webbing can create a strap over your shoulder or surrounding your hips, you can use that combined with a large Carbiner to bring down the kite, dragging it out of the center of the window as you go down-wind
Sand anchors are easy to set-up and light weight to remove afterwards,
most friends sew a square tarp in an "X" with more seat-belt webbing as the across striped members, then use those four new corners to pinch the sand beneath and hold the kite (yes w/a larks head knot too!). Recommend you put an extra or TWO behind that first one, just in case of failure.
Check with some big kite inflatable fliers like Andrew Beatty from the UK for more particular help and accessories to simplify your efforts, increase the safety measures.