Hi Wolfgang,
This sounds like it would be a useful feature and since NWBC stores favourites locally, should not be that hard to implement. Can I suggest you add it to this NWBC Feature Request and Improvement Register
No guarantees that it will make it into the product but worth a go, hopefully the NWBC product owner takes a look at that list for inspiration from time to time 
Have you tried manually copying favourites and changing the SID...? Does it work?
Thanks,
Simon