d3 v4 brush & zoom with two fingers touch

I have applied zoom to a selection in my d3 charts using d3 brush based on this example http://ift.tt/2juXzaV but this does not support the brush selection with "two fingers" on mobile (touch event with e.touches.length). How can I handle the brush event of the brush in d3 to handle this event to select the area inside the touches in mobile without rewriting all the brush handler defined in d3-brush ?