Hey, I'm MechaBlade. I used to write scat stories, but I don't much anymore. Most of the scat stories revolve around women being forced to shit while men are watching, though never on a person. One of my best reviewed stories is "Ashley's Little Show", where terrorists force a student to shit in front of the class.

Not sure about gurochan's linking policy so let's see if this works: http://www.asstr.org/~mechablade/stories.html#scat