Sorry, just went through and double checked with an actual customization, I don’t think applying a CSS rule will be enough since the div ids are, I guess, generated by ember, and are in any case not constant. Maybe there’s something you can do with javascript? Would have to ask someone else though, unfortunately.
What I get for writing out a quick solution without paying enough attention. 
I don’t know that there’s a setting for what you’re looking for, renaming the user to something innocuous would at least be the easiest thing to do.