(Edit - My post was merged from a separate comment I made and did not realize this idea was already posted.)
I have one suggestion with 2 possible ways to implement it.
#1 the ability within a wall type to add a selected line type that overlays down the middle to identify firewalls.
taking this idea step further I would ideally like to see #2
#2 essentially the same thing but a drop down for the FIRE RATING property under IDENTITY DATA in the Type Properties of the wall. Once you select the desired rating it could automatically add the associated line type. Would probably be idea of this drop down could be edited under ADDITIONAL SETTINGS. Were you could customize the list of rating, and the associated line types to identify.
They way we have been addressing this until now has been to great a group for the entire floor with the desired line types that are aligned to the center of the wall. The issue is if the walls move we then have to edit the group to realign them.