Warning, this is stream of conciousness, untested and not approved by the FDA for general use on humans.

You might be able to simulate this by putting your NIC in promiscuous mode and sniffing for the packets with the multiple MAC addresses you want. A quick search on CPAN seems to show a number of modules to impliment a TCP/IP stack so one might actually be able to pull something like this off. You've got to fake out the routers, and since MAC addresses need to be unique, you could, however unlikely, colide. It sounds like a bit of an undertaking to me. But it's the only thing I can think of that might come close to what you're looking for.
Good luck though.

Ira,

"So... What do all these little arrows mean?"
~unknown