Well, any sort of glue is out due to their massive size. Sewing could still be possible, but you'd probably have to attach them to a really solid piece of material for that to work. Like a thick vest or something that hugs your body so they are balanced. Have you considered buying some black suspenders and attaching them to those? You could rig something up almost like the gear on attack on titan. Since he wears black the suspenders would match and not cause too much focal point.