I have given some thought to this matter and do recall that many people on the Master-Cleanse diet and taking the shake have mentioned passing the stuff. Of interest is the fact that they usually mention that the gunk they pass is black. The lemonade/cayenne mixture along with psyllium wouldn't produce black, rubbery, voluminous stool, I don't think.
BTW, PTree, I believe the dispute was not over the existence of MP but whether or not psyllium mimics it. Correct me if I'm wrong.