Hiho,
yesterday I was installing and playing a while with Knights of Honor again (older game, but some of the mechanics are nice) 
This catched me to one of the following ideas - and I don't know if this is possible or not:
There should be an option to turn an own champion into a Spy. For every turn as a Spy a small fee on Diplomatic Capital has to be paid. For other players/AI this champion is looking like a neutral Champ everyone can hire (and therefore can freely move around). If this Champ is being hired by another player/AI, this champ gets controlled by the other player, which would increase the DC cost of the spy BUT with the following options/benefits:
* The 'owner' of the spy still is able to see all the movement and actions done by the spy.
* Additionally, the owner of the spy has the following options available:
- Moving with an army, there should be the option to disband/lower the morale of the army. Choosing this option, a portion of the army will disband or will have a lower morale
- Being station in a city, there should be the option to raze some random improvements, increase unrest if this will be implemented somewhen or decrease the overall income of the city for an certain amount of turns.
After the action has been choosen, the Champ will vanish (as he will not be of use anymore and the traceability should not be given).
I don't know if such an option is even possible - but would be cool if it would be there 