Idea for a random event

Been playing X2: the threat for the past few months. And in this game they have BBS mission you can take on for extra money. Well one is the revenge missions where X race asks you to kill a rogue enemy. I was thinking this would be a good random event for Civ 4. Say you get it if you meat certain economic and military requirements etc. But the message would go something like Rogue militia men from England(etc.) have been spotted near Nottingham. He is seeking refuge in the outlands of the Zulu. The English authorities are offering 400 gold for capture or proof of their demise. The game would then spawn the appropriate Barbarian unit for that era with it just having orders to get to a rival civs border and then it will vanish. If the player can kill it before other civs do or before the unit makes it to safety they get 400 gold and a relations boost with the offering Civ. If it makes to safety then they fail and lose relations with the offering civ. Is this even possible?

there's an Event, where you get a reward for capturing a city with a special resource in the fat cross.
If you could change the resource/the city to an unit, it would do, what you want.
But i think, this is more difficult.