Maybe Heroes could semi-randomly show up in battle reports with their actions? Doesn't really need any mechanics behind it, just provide a small chance for any hero in the battle to be mentioned by name for personal actions, rather than just his unit. You could boost the chance slightly for sieges or something.
This doesn't require more mechanics but would add some flavor. Just seeing the name of your hero character mentioned at the moment of an important breach/charge/defense (and knowing the realms involved see it too) could be enough
look at how Sandalak has been compiling reports on which unit has inflicted wounds on/captured/killed enemies, people like the spotlight.
