Inserting a XSER field in UCP4

[Pong]

hi, given that the SMSC is using CMG UCP/EMI4, 
when replying to an SMS message or sending an SMS-Push message,
how do we insert a XSER field type (billing identifier) in the
message packet where the XSER field data in hex
format is 0CLLDD where

        LL - length of data
        DD - data in hex format

thanks,
pong