I would go in the KNDEF and modify the ISDNSK (number of digit to skip)
I work with 4 digits extensions
i.e ADD-KNDEF:NNO=1-41-225,TYPE=OWN,ISDNCC=41,ISDNLC=22562,ISDNSK=0,ISDNUL=EXT,PNPLC=370,PNPSK=3,PNPUL=L0;
here 0 digit to skip because the numbers the num I receive is
+41 22562 XXXX...