Have u tried £-stretcher/instore for them they ve got all sorts of different ones down there that mite be some use to u, i used to get the same trouble well i still do but i had a great pair from down there as i used to jog around the field wen walking the dog, its so annoying isnt it cos u feel stupid when they keep falling out!
hope u have some joy with them soon,
love fanargadeb