Gold Bounty from non-creeps?

I've got a computer-controlled player with units like footmen. I want the heros to get gold when they kill these footmen. I want it to put +20 or whatnot over the unit that dies. I know killing creeps does this, how do I get it to work on other units? I guess I could classify every single unit type as being 'Neutral Hostile', but what about heros? Is there another way? Help?

Thanks in advance...

Triggers. If you need a more detailed response than this, say so, I'll give it.

SET PLAYERS FLAG ON !

Player - Turn Gives bounty On for Player 12 (Brown)
--> all players will get gold from killing player 12's units.