Till I find a solution (same you are looking for, mentioned above), I add the specific css file with the additional css lines in a separate header which is called from the template that needs the additional css lines.(working with 3 different templates for postings therefore it works as a temporarily solution)
Having also a code snippet (in sandbox) which enqueue an external css file but that loads it just (same as you mentioned above)in same style.css
Looking for a fancy way so it only loads in templates which need that specific css.
Shea is master in doing real code so I am curious and hoping :)
His code-snippets plugin is also awesome so who knows.
note: didnt want to interfear but had same question in mind.