IDOC to EDIFACT with envelopes

Please this is urgent,

I have to map IDOC to EDIFACT document and generate envelopes.Service wm.b2b.edi.util:addICEnvelopeEDIFACT is used to add UNB/UNZ envelope but how are we supposed to add UNG/UNE envelope. I cudn’t find any service for this in BIS guide.

Thanks in advance,