I suggest:
every unit has a 'reputation, skillset, organization' that can be described with an adjective or two. Each player would qualify each of their units with some adjective. This shouldn't be something like 'super killers' or 'long-distance fighters' but more like things like: 'hard-drinking', 'disciplined', 'lax', 'fool-hardy', 'camping enthusiasts', etc. I would also give them each an adjective (like i would give the Hippus Blades of Camuos: 'fearsome' and the Shield of Kylorin: 'treacherous').
These would not really be promotions but i would take the adjectives into consideration when battle is fought with them. If they do something to really make themselves stand out they could change thier adjective (think: cowardly, brave, stealthy, ignorant, etc) or add a new one.
What do people think? it wouldn't have too great a game effect but there would be some effect (no more then a +1/-1 to the dice).