Just recruit the bare minimum of men (Usually 5 but for RCs that have less you can recruit even fewer. My favorite is the SF that only drafts 1 per day. In which case, you have a single soldier standing by your side as you rush into battle.)
The way it works is that generally, a hero can only die in battle after receiving a second "wound" that acts as the killing blow. This might not necessarily always be the case, as I asked once, and was told that a hero can die in one hit depending on his current status. But I'm pretty sure you can't die in one hit when you're in the "Ok" status. In that case, just bring 5 or fewer men along at all times, set to minimum retreat, and have fun watching your unit die all the time. But hey, that means you're not dead.
Another alternative is to go unitless. While this seems pointless, do not underestimate the ability of heroes to tell tales and escape from prison every turn. Furthermore, they don't affect Courtier abilities, nor Priest abilities, both of which are main classes.
