I agree with the idea, being able to do it while stationed in the city of origin makes perfect sense. But I doubt it's a popular measure , you just look at how players from the biggest alliances are always leaving and coming back to gain combat points with troops that are being recruited just for that. Killing former allies' troops may be the most common way to get battle points.
If you don't have an alliance you can always arrange with any other player near you to send the troops you don't want against him or send them to a small town and wait for death. He sure appreciates the extra points and you have the problem solved.