Is there a way a send custom (and event undemanded) arp responses via shell (e.g. by hand or by a shell script) on MacOS X or any other UNIX? In addition, is there a way of making the software ask for the MAC representation for all IPs in the current subnet without sending pings the anyone?
A packet generator might do the trick. The wikipedia page links to some implementations but I don't know if they work on OSX.