I wrote a tiny Minecraft mod for the 1.2.5 server. It's not a bukkit plugin, just a regular mod to the official minecraft_server.jar. So I doubt anyone will bother to try it.
My mod adds a new drop to Endermen. If an Enderman is killed by a Zombie Pigman, the Enderman will drop Record 11.
You might wonder how this fight could ever happen in the first place. Well, my mod also adds the ability for Zombie Pigmen to look at Endermen like players do. And this angers Endermen, just like when players look at them, which causes the Enderman to attack the Pigman.
If the Pigman manages to kill the Enderman, then you get your record.
Normally, a Pigman will never spawn near an Enderman. But it is possible. Yes, you can spawn them together in Creative Mode. But beyond that, you may be aware that it is possible for a Pigman to spawn if a regular pig is struck by lightning.
Also, Endermen are more powerful than Pigmen. It takes about three Pigmen to kill one Enderman.
So if a Pigman ever spawns by lightning, it's a good idea to damage the Enderman before getting them together, since it's pretty much impossible to get enough Pigmen to do the job without help. Or maybe you can buff the Pigman and poison the Enderman with potions before the fight.
Pro-tip: A Pigman is more likely to look at an Enderman if the Enderman is standing between a player and the Pigman.
So it's not an easy task, but I'm assuming it is possible, though I've only tested it with spawner eggs.
