I don’t think that there is an oral substitute for 21 Hydroxylase.  I am sure if there were, no matter what you supplement with, either too little or too much of any enzyme or hormone would cause too little or too much production of the hormones that follow anyway in the metabolic pathways.  It would be just as much a balancing act replacing 21 Hydroxylase therefore as it is replacing cortisol I should think in that case.