Missing UNB and UNZ segments in D95B Codeco EDI Schema!

Hello,

I need to use the D95B Codeco EDI Schema in a map but the UNB and UNZ segments are missing from this schema. I read on the net that these segments have to be added in the pipeline using EDI Schema extensions and/or envelopes. How do I go about adding these two segments to the shipped EDI Codeco schema without invalidating it?

Thanx a lot for your answers.