a little trick that may help if you sense that you are going to have a really big large as in width bm - so as to help minimize the stretch - is to apply pressure with your fingers the areas around the anus so that you can help shape the width of the bm coming out and minimize the stretch.
also, if you go back to squatting, the squatting method will help alleviate the pressure on the anus and make the exit much much more tolerable.