they are not accounts. I know
@Vitor Pamplona calls them that, but that is because he is crazy and can't be reasoned with.
On a different note; at some point your scenario becomes such it just requires a different client to facilitate your usecase.
One thing i can see usefull for something geared towards multi-profile setups is a prompt before posting asking you which one you want to use for a post, instead that decission being made semi in the background up front.
A settings environment where you can select what scheme should apply to what set of profiles is also something you would probably see in such a client