Required:  One laptop bag strap or other flex-mesh, wide strap.  Also:  Extreme caution.

Seeking a longer term stretching than 3X30 seconds, but perhaps at a lower intensity.  Configure the strap like an old book strap - place the loop under your heel and knee, set the strap in the back of the knee and the other end around the ball of the foot. 

Tighten the loop until the strap stays in place - maybe this won't work for skinny people - and tighten until the ankle flexes and the ball of the foot is pulled back toward the knee.  Excess strap end can be used to crank this down a bit for more stretch but should not be done for long.   I have the excess end coming off mid-calf height, i pass it around the other side of the strap and under so friction will hold it.

Will be test driving the low intensity stretch with attention to any abrasion or circulation problems being prevented.