Here would be my list. Not to imply you're not already doing these things:

1. Verbal high-fives. Either on cb or to individual characters. Possibly in the guise of one of the cabal mobs. I remember Enlilth doing this once for some Empire bard who was sort of newbieish and had just gotten destroyed by Fortress during a raid. But at least he had tried to defend. Enlilth popped down and promoted him on the spot. I think he may also have given him black sanc, which wasn't as cool, but the dude was so outnumbered I didn't feel it was inappropriate.

2. Doing the sort of policing mortal leaders can't do. Booting people for being idiots. It's frustrating for a mortal leader when he really suspects someone's doing something boot-worthy but can never verify it because he's just not able to watch the guy 24/7. On the other hand, having the cabal imm do this sort of kills the possibility of characters playing "treacherous" roles, e.g. corrupt tribunal.

3. Quests are kind of cool, even if they're short-term and pretty simplistic. Using Enlith as an example again, the one where he "stole" Padwei was fun. Was interesting to see everyone's different reactions.