Anne Marie is right about this.  The reason why it is not possible to just replace the missing enzyme is because there are different kinds of enzymes.

Some enzymes, like digestive enzymes, exist outside of the cells.  The enzymes involved in CAH (e.g. 21-hydroxylase) exist within the cells.  In order to replace those enzymes, you have to deliver them into the cell.  This is not possible via ingestion.