I think I pulled this off reasonably successfully today. I figure if my bowels act up during a marathon I need to be able to do it.
So I just gave the back of my racing shorts a quick downward tug, let it go, and pulled back up. It felt a little messy and chafing over the rest of the run, but it was so much better than a straight-up pants pooping.
I realize it was kind of anti-social and the people in the neighborhood I was running through really won't appreciate it. I will make up for it by being super socially responsible in other areas of my life.
If I have to do this during the marathon of course it will be awkward, however:
-I am fast enough there will not be a huge train of people right behind me
-Paula Radcliffe did this, I should be allowed to do it also
I am planning to run in the 2:2x range, which I will argue is fast enough that I can be forgiven the fact I did not want to lose time in the port-o-pottie.