as a Clark Protocol enthusiast for over 10 years my overview is that we're talking about two different things here.
you don't really need the enema to clear your colon, BUT: a coffee enema is a totally different concept than emptying the colon, which the Epsom Salts will do, since the coffee is a liver cleanse protocol, and NO, not gall stone cleansing, just general liver cleansing. A coffee enema will rid your system of a lot of debris that you won't get from a simple Colon Cleanse enema.
I believe that a coffee enema the day before the Flush routine would facilitate the stone removal.