As long as our nobles are doing hard time lets think about some other things:
-Getting into fights while in prison.
-Starting prison riots, an option available to heroes or infiltrators. Breaking out via riot gives you a small unit of random soldiers from your realm with really high cohesion.
-Limited training options. Not as good as an academy but maybe you can find a tutor who's willing to show you a few things count of Monte Cristo style.
With stuff like this I'd almost want to get captured.
