I seem to look for difficult solutions and get so fixated on that path that I can't see alternatives - I have to do it this way!
When looking to even up the placement of my post permalinks I ended up using jQuery to dynamically apply a class to an element.
Matthew Roach suggested looking at it a different way by changing the CSS and applying a condition to the first paragraph in a post.
But it just dawned on me, in a rare moment of clarity, that I could just directly target the last paragraph in a post via CSS - no jQuery required:
.entry-content > p:last-of-type
You live and learn.