I found this while screwing around in RA2 today.
Go to Exhibition and start a 4-player match.
Put a bot in the one player slot and one in the 4 player slot.
Then change the fight type to deathmatch.
Change the arena to the Battlebox. DO NOT GO BACK TO THE BOT SELECT OR ELSE IT SCREWS UP.
Then start the match. the player 4 bot will be floating in space somewhere, and eliminate itself soon.