Umh, does
UI stand for
User Interface?
If so, then
dismissing isnt a UI problem, imho: Just add a "get lost"-command, which tells a commander to drive his assigned troops away during a fake maneuver in the woods. The commander should then go away himself by a percentage chance based on the troops' experience points, because of his bad remorse due to disbanding his loyal servants...
(Oh, wait, this would also implement another new option: the option of resigning a game, if you give this order to your pretender...
)