Simple Answer: If you're receiving the calling line ID (CLID), and you have vectoring, then yes:
......................................
goto step x if ani = nnnnnnnnnn
step x:
busy
......................................
This will provide busy treatment to any caller calling from that calling line ID.
If you're not receiving the CLID, reply with the mode in which the caller is contacting you (DID, toll-free number, extension off main number, etc.) and indicate whether you're able to ID the caller prior to call answer.
Basically, you need to be able to identify the caller, and then provide treatment unique to just that caller...