How about a possibility to rescue an lord from the city prison? There would be a few ways to accomplish this:
First, you have to inform the lord about the escape plan by going into the dungeons (By bribing the guard), and you have 2 options after that:
1) You wait until the night comes and guards are switched. On his way to the town barracks, you attack him. Then we come to the battle screen, where you have to defeat the guard. When you do, the screen changes and it tells you that you have the prison key and have freed Lord [Insert name here] before a new guard arrives.
After that, there is a random chance that you are encountered by more guards and have to fight your way through them. This time you will have the freed lord fighting besides you, armed with fists/maybe a weapon got from the dead guard?
Or, an alternative way:
2) You have to bribe the city guard in and near the prison, with a moderately large amount of money (1-6k denars, depending how important the lord or king is.), which allows you to free the Lord and leave the city without problem.
Some other lords/kings/khans could also give you a quest to do this, but it would be possible anytime. (Like the "Save the village from marauding bandits" quests.)
After leaving the town, the lord leaves your party and materializes in a friendly castle in a few days. Like the freed lords and kings always do.
Then to another suggestion: It is possible that all those companions you can hire could also be hostile? Like, they could join an enemy army and fight alongside them, or even ally with bandits, sea raiders, mercenaries and such. This would be even more likely if they have left your party sometimes and have bad memories about your company and the possible faction you belong in. Also depends on their personality.
Then you could beat them and take them as prisoners, like lords and such. I have no idea what to do after that though. You could persuade them to join you, like normal prisoners..
But it would be a great thing anyways.