After the custom path has been created all the way to the dim or fact (non-history) table, add the extra required xx_ prefixed columns to that table. In the column definition, do not give the new xx_ prefixed custom column a source table; it should be blank. Transform those column values to some dummy value and then build a procedure with an xx_ prefix that updates the new custom xx_ columns after the table is populated during its normal load process. Below is an illustration of what the resulting diagram is for a parallel path effort for the dim_item table.