Morbid Minish
Spooky Scary Skeleton.
Looking into this one the only available addon I can see is here which is quite expensive for the limited functionality it provides. It also doesn't seen to allow anon posting only in certain forums or have a clear indication of just how anonymous posts actually are. From the discussion thread it seems that posts that were supposed to be anonymous didn't come out that way so I am hesitant for all those reasons to go with this option. While I think this could be a good idea it doesn't seem feasible right now with what is available out there unfortunately. While I know this isn't the same and isn't entirely anonymous I think that there shouldn't be a problem posting threads on behalf of another member if someone wants to have a trusted mod or friend post something on their behalf. Obviously this isn't ideal but for now it may be the best solution that can be provided.
I thought of something for this but I'm not sure how much of a pain it would be to do. I know for the anonymous mafia game you were able to restrict the accounts to only be able to access the mafia section. I thought maybe something similar could be done with Life Advice, where maybe users could apply to create an alt account that would only have access to the Life Advice section. It would allow other users to also reply anonymously in case their advice contains stuff they wouldn't want to share on their normal accounts. The main issue I see is just the extra amount of accounts that would be created, and then setting up the perms for each one.