It's not what the user as asked...MikroTik has a ftp server imbedded
you can access to ftp server via command prompt in windows or shell in Linux
type ftp/? in windows to get help command
then write an batch file to access ftp server(mikrotik).schedule file to get file and copy it to local system
and also write a script to delete captured packet.
It comes to my mind,a time consuming process!